i®
PROGRAMMING
YOUR
ATARI
COMPUTER
BY MARK THOMPSON
No. 1453
$16.95
PROGRAMMING
YOUR
ATARI® COMPUTER
BY MARK THOMPSON
TAB
TAB BOOKS Inc.
BLUE RIDGE SUMMIT, PA. 17214
FIRST EDITION
FIRST PRINTING
Copyright © 1983 by TAB BOOKS Inc.
Printed in the United States of America
Reproduction or publication of the content in any manner, without express
permission of the publisher, is prohibited. No liability is assumed with respect to
the use of the information herein.
Library of Congress Cataloging in Publication Data
Thompson, Mark S.
Programming your Atari computer.
Includes index.
1. Atari 800 (Computer)— Programming. I. Title.
QA76.8.A814T46 1983 001.64'2 82-19334
ISBN 0-8306-0453-7
ISBN 0-8306-1453-2 (pbk.)
Contents
Preface vii
1 Number Systems and Codes 1
The Decimal Number System — The Binary Number System —
Converting Decimal Numbers to Binary Numbers — Converting Bi-
nary Numbers to Decimal Numbers — Octal Number System —
Hexadecimal Number System— Binary Codes
2 Microcomputer Basics 12
Computer Structure — Software — Interconnection of Elements —
Scaling of Computers — Microprocessors — Computer Bus
Systems — Types of Storage — Bus Control of I /O
3 Computer Arithmetic 31
Addition and Subtraction of Binary Numbers — Multiplication and
Division of Binary Numbers — Fractions and Decimals
4 Boolean Operations 44
Boolean Algebra — Classes and Elements — Venn Diagrams —
Connectives and Variables — Applications to Switching Cir-
cuits — Fundamental Laws and Axioms of Boolean Algebra —
Boolean Equation Simplification and Mechanization
5 Introduction to Programming 80
BASIC — The Programming Process — Let's Write a Program —
Line Numbers— BASIC Statements
6 Introduction to the ATARI 800 97
Understanding Software — Keyboard — Program Recorder —
Learning to Program the ATARI 800— Writing BASIC Source
Programs — Editing Your Program — Transferring Programs to and
from Cassette Tapes
7 Optional Peripherals and Software 119
8K Computer Systems — The Printer — 16K Computer Sys-
tems—Controllers—The ATARI 810 Disk Drive — Disk Operating
System— BASIC Commands Used with Disk Operations-
Directory of BASIC Words Used with Disk Operations— BASIC
Error Messages Used During Disk Operation
8 I/O Operations 135
Input /Output Devices— Input and Output Commands
9 Mathematical and Other Functions 143
Arithmetic Functions— Trigonometric Functions— Special Pur-
pose Functions
10 Programming Techniques to Save Memory 147
1 1 Sample Programs: Conversions 149
Currency Exchange— Metric Conversions
12 More Programs 157
Finding Greatest Common Divisor of Two Numbers— Program for
Gun Collectors — Checkbook Balancer
13 Flowcharting Techniques 165
Flowcharting Symbols — Control Structures — The If Statement —
The Else Option — Pseudocode
14 ATARI Graphics and Sound 174
Commands to Control the Graphics — Text Modes Character Print
Program — Light Show Program — United States Flag Program —
Video Graffiti — Using Sound — Type-a-Tune Program — Computer
Blues
15 Programming in Machine Language 198
16 Continuing Education 205
NRI— National Technical School— Typical Correspondence
Lessons
Appendix A Alphabetical Directory
of BASIC Reserved Words 220
Appendix B Error Messages 226
Appendix C ATASCII Character Set 229
Appendix D ATARI 400/800 Memory Map 234
Appendix E Derived Functions 237
Appendix F Printed Versions of Control Characters 238
Appendix G Memory Locations 239
Appendix H Glossary of Microcomputer Items 242
Index 270
Preface
This book is directed to the person interested in obtaining a com-
plete understanding of the design and capabilities of the ATARI 800
computer. It opens the door to many applications of the ATARI 800.
It differs from many books in that it explains fundamental micro-
processor techniques while it enables you to use your own ATARI
effectively .
Software packages are available that will enable the user of an
ATARI 800 to begin running programs without spending time
learning the basic fundamentals. However, to write and run pro-
grams effectively, the programmer should have a fundamental un-
derstanding of the components that make up the ATARI 800. This
knowledge begins with the microprocessor chips, memory chips,
and I/O chips . It extends to the keyboard and switches for setting up
an instrument or device, transducers for sensing inputs, actuators
for control, devices for communicating with remote computers and
other instruments, devices to provide extra storage capability, and
printers and displays for informing the user of results.
Once the basic components of the machine are understood, the
programmer must thoroughly understand programming processes
and be able to translate these into the language of the ATARI 800. It
is also helpful for the programmer to understand how the extensive
requirements of the ATARI 800 can be broken down into manage-
able parts and how sections of programs can be written to meet each
requirement. Finally, the programmer must be able to put the
vii
software parts together into a coordinated whole so that the overall
goals of the program are met.
To the novice, all of these requirements may seem a little
much to conquer right at the beginning, but this book is designed to
lead you step-by-step— taking first things first— until even the
beginner will be able to program the ATARI 800just like a seasoned
pro.
Some of the initial data may seem immaterial at first , but as you
get more and more into actual programming, all of this material will
"gel"— and result in a thorough knowledge of the ATARI 800 and
how to program it to suit personal needs.
Chapter 1
Number Systems and Codes
Binary numbers and codes are the basic language of all micro-
processors—including the ATARI 800— and a good, solid founda-
tion in these numbers and codes is essential in understanding how
microprocessors operate and how they are programmed. A good
knowledge of octal and hexadecimal numbers is also important as
they allow easy manipulation of binary numbers and data. Under-
standing these systems thoroughly will give you an excellent
working knowledge of the codes used in programming the ATARI
800.
THE DECIMAL NUMBER SYSTEM
All of you are familiar with the decimal number system as this
is the system you were introduced to when you first started to learn
mathematics . You may remember that this system has a base , which
indicates the number of characters or digits used to represent
quantities, of 10 (the numerals zero through nine).
Other number systems also have bases, but they differ from
each other. In fact, the base (sometimes called radix) is the basic
distinguishing feature of all number systems. When necessary a
subscript is used to show the base. To illustrate, the number 1982 10
is from a number system with a base of 10.
Each digit position in a number in the decimal number system
carries a particular weight which determines the magnitude of that
number. Each position has a value determined by some power of the
base, in this case 10. The value of each 10°, 10\ 10 2 , and so forth.
Condensed, they are as follows:
10° =
1
10' =
10
10 2 =
100
10 3 =
1,000
10 4 =
10,000
10 5 =
100,000
10 6 =
1,000,000
10 7 =
10,000,000
10 8 =
100,000,000
10 9 =
1,000,000,000
It is easy to see that for most uses , we seldom have the need to
go higher than 10 9 — except to balance our national budget!
The small figure used to indicate the power to which a number
is raised is called an exponent , and the number raised to that power
is called the base number, or simply the base . Thus, in the previous
example, 10°, 10\ 10 2 ,etc, the number 10 is the base, and 0, 1,2,
3, 4, 5, 6, 7, 8, and 9 are exponents.
The total quantity of a number is evaluated by considering the
specific digits and the values of their positions. For example, the
number 6403 is meaningful as written, but it may also be written in
positional notation as,
(6 x 10 3 ) + (4 x 10 2 ) + (0 x 10 1 ) + (3 x 10°)
which equals,
(6 x 1000) + (4 x 100) + (0 x 10) + (3xl)
or,
6000 + 400 + + 3 = 6403
In other words, to determine the value of a number, multiply each
digit by the value of its position and add the results.
In the previous examples , only integer or whole numbers have
been discussed. Sometimes, however, it becomes necessary to
express quantities in terms of fractional parts of a whole number.
We must then use numbers whose positions have values that are
negative powers of ten. A partial listing of negative powers of 10
are:
io- ' =
1
10
io- 2 =
1
100
10- 3 =
1
1000
IO" 4 =
1
10,000
10" 5 =
1
100,000
io- 6 =
1
1,000,000
or 0.1
or 0.01
or 0.001
or 0.0001
or 0.00001
or 0.000001
We could continue, but the point should be clear for our purposes.
You also know that a decimal point separates the whole and
fractional parts of a number. The whole number is to the left of the
decimal point and the fractional part is written to the right of the
decimal point. To illustrate this, the decimal number 3.17 can be
written with positional notation as follows:
(3 x 10°) + (1 x IO" 1 ) + (7 x 10" 2 )
which equals,
(3 x 1) + (1 x 1/10) + (7 x 1/100)
or,
3 + .1 + .07 = 3.17
In the example above, the left-most digit (3 x 10°) is the most
significant digit as it obviously carries the greatest weight in deter-
mining the value of the number. The number to the far-right of the
decimal point is the least significant digit as it carries the least
weight in determining the value of the number.
THE BINARY NUMBER SYSTEM
The simplest number system that uses scientific notation (ex-
ponents) is the binary number system, which consists of only two
elements , and is expressed as a base of 2 (0 and 1) . These two digits
have the same basic value as and 1 in the decimal number system.
Because of its simplicity, microprocessors use the binary
number system to manipulate data, which is represented by binary
digits called bits. The term "bit" is derived from the contraction of
Table 1-1. Decimal and Binary Positional Values.
Decimal 10 3
1000
10 2
100
10'
10
10°
1
Binary 2 3
Value expressed 8
in decimal
Value expressed 1000
in binary
2 2
4
100
2'
2
10
2°
1
1
binary dig//. Microprocessors operate on groups of bits which are
referred to as words. The binary number 00001101 contains eight
bits.
When dealing with the binary number system, it is very im-
portant not to confuse the numbers involved . The binary number 10,
for example , should be thought of being "one , zero" and not "ten" as
it would in the decimal number system. Ten has no meaning in
binary notation. Similarly, the binary number 100 should be thought
of as "one , zero , zero" and not as "one hundred ." Always think of the
binary numbers as "ones" and "zeros."
Note that when you are dealing with several number systems,
it is best to identify a number with an appropriate subscript. For
example, the notation 10 identifies the number as being in the
decimal system (base of 10) and the number is "ten." The notation
100 )0 would be "one hundred." The notation 100 2 is "one, zero,
zero" in the binary system; 100 g is "one, zero, zero" in the octal
system; and 100 is "one, zero, zero" in the hexadecimal system.
The latter two systems will be discussed later in this chapter.
In the binary system, you will either multiply 2° by one or by
zero, as we are using only two numbers. The positional values in the
decimal and binary systems are shown in Table 1-1 . Notice that the
power to which the base is raised is the same in both systems. To
better understand these positional values , let's express decimal 1 in
binary numbers. Binary 2° = 1, and one times 1 equals one. There-
fore, decimal 1 equals binary 1.
Decimal 2 expressed in binary numbers means that we move
over into the next position in Table 1-1 and find that by multiplying
2 1 by one results in 10 or "one, zero" equals decimal 2.
CONVERTING DECIMAL NUMBERS TO BINARY NUMBERS
In programming the ATARI 800 and other microprocessors,
you will often need to determine the decimal value of binary num-
bers. In addition, you will find it necessary to convert a specific
decimal number into its binary equivalent.
The chart in Table 1-2 gives the decimal/binary equivalents for
numbers from to 16. This would be very helpful if they were the
only numbers encountered in programming. Actually, this is not the
case; you will need to convert many different numbers and an easier
method must be used. Since a binary number is based on powers of
2, we can convert a decimal number to binary by repeatedly dividing
by two.
To simplify matters, let's take the number 10 . Set up your
division as follows:
2 1 10
2|5_
2[2_
2 li
1010
Notice we first take the number 10 and divide by 2 . Two goes into 10
five times with a remainder of zero. We write the 5 beneath the 10
and the to the right of the vertical line. Now divide 2 into 5, it goes
two times with a remainder of one . Write the 2 beneath the 5 and the
remainder 1 beneath the to the right of the vertical line. Divide 2
Table 1-2. Decimal/
Binary Equivalents.
Decimal
Binary
1
1
2
10
3
11
4
100
5
101
6
110
7
111
8
1000
9
1001
10
1010
11
1011
12
1100
13
1101
14
1110
15
1111
16
10000
into 2; it goes 1 time with a remainder of 0. Write the 1 beneath the 2
to the right of the vertical line. Finally, divide 2 into 1; it goes
times with a remainder of 1, so write the remainder to the right of
the vertical line. The digits to the right of the vertical line are the
binary equivalent of the decimal number. The number is written
from right to left working from top to bottom, or from left to right
working from bottom to top. Therefore, the binary equivalent of 10
is 1010, as listed in Table 1-2.
The same procedure can be used no matter how large the
numbers . Just continually divide by 2, placing either a or a 1 to the
right of the vertical line. If you haven't tried converting decimal
numbers to binary, work a few examples from numbers, say, 12 to
16 and then check your answers with Table 1-2.
Example of this type of method (using fractions) is shown in
Table 1-3. The decimal fraction 0.90625 is continually multiplied by
2! Did you say multiply? Yes, to convert a decimal fraction to a
binary number, multiply the fraction successively by the desired
base (two in our case) and record any integers produced by the
multiplication as an overflow. These calculations will result in
numbers with a 1 or in the units position. Subtract the unit and
multiply the rest by 2 again. The decimal fraction 0.90625 is con-
verted as follows:
Table 1-3. Converting Decimal Fractions to Binary. Note That the
Original Number Is First Multiplied by 2, the Product of which is
Multiplied by 2, and so on Until the Number Comes Out Even. There
Will Be Times, However, Where the Number May Not Come Out Even— Just
Like in the Decimal System. But All Can Be Carried Out for Practical Accuracy.
0.90625
x 2
= 1.8125
= 0.8125 with overflow 1
0.81250
x 2
= 1.6250
= 0.6250 1
0.6250
x 2
= 1.2500
= 0.2500 1
0.25000
x 2
= 0.5000
= 0.5000
0.50000
x 2
= 1.0000
= 1
Notice that the multiplication process is continued until either or
the desired precision is obtained. The overflows are then collected
beginning with the most significant value, which is the first digit to
the right of the binary point, and proceeding to the least significant
value. The number is 0.11101 2 .
If the decimal number contains both an integer and fraction,
you must separate the integer and fraction using the decimal point
as the break point . Then perform the appropriate conversion pro-
cess on each portion. After you convert the binary integer and
binary fraction, recombine them.
CONVERTING BINARY NUMBERS TO DECIMAL NUMBERS
The easiest way (and the way recommended initially) to con-
vert binary fractions to decimal numbers is to use a table, such as
the one shown in Table 1-4. To use this table, let's take a number,
say binary 1011010 and convert it to its decimal equivalent. There
are seven digits in the number 1011010. The first 1 (the digit
farthest left) is in the 2 6 column and is equal to the decimal number
64. There is a zero under 2 5 , so there is nothing taken from this
column. Under 2 4 there is a 1, so we write the value 16 next to our
previous number 64. There is a 1 in the 2 3 column, so an 8 is placed
next to the 16. In the 2 2 column there is a 0, and therefore, the value
will be omitted. But there is a 1 beneath the 2 1 column and this
means a 2 is placed next to the previous 8. There is a beneath 2°,
so we omit this value also. Now the numbers 64, 16, 8 and 2 are
totalled for a sum of 90— the decimal number equivalent to
1011010.
Refer again to the table in Table 1-4 and follow the description
of the conversion step-by-step until you are certain that you under-
stand how the conversion was made . Then practice some conver-
sions of your own . Check your answers by reversing the conversion
process; that is, use repeated divisions (or multiplications, de-
pending upon the case) by 2.
OCTAL NUMBER SYSTEM
Octal is another number system, this time with a base of 8. It
uses the digits through 7, and these have the same basic value as
the digits through 7 in the decimal number system. Actually , octal
numbers are really nothing more than 3-bit groups of binary num-
bers. In fact, octal numbers are a form of binary shorthand.
To convert a binary number to an octal number, first write
down the binary value and, starting from the right-hand end of the
Table 1-4. Table for Converting Binary Fractions to Decimal Numbers.
2' 1
0.5
2~ 2
0.25
2 -3
0.125
2' 4
0.0625
2" 5
0.03125
2- 6
0.015625
2~ 7
0.0078125
2 -8
0.00390625
2" 9
0.001953125
2 -10
0.0009765625
Table 1-5. Binary-to-Octal Conversion.
Octal
Binary
000
1
001
2
010
3
011
4
100
5
101
6
110
7
111
01
1
010
2
110
6
011
3
(binary)
(octal)
number, mark off groups of three bits. Now, using Table 1-5, write
down the equivalent octal value in each group. Notice that this
conversion is exactly like binary-to-decimal conversion, except that
the decimal digits 8 and 9 don't exist in the octal system.
Converting a decimal number to octal is accomplished in the
same manner as decimal to binary except that the base number is
now 8 rather than 2. Therefore, write the decimal number and
divide by 8. For example, to convert the decimal number 469 to
octal, set up your division as shown in Fig. 1-1. Note that the
decimal number 469 is equal to 725 octal number . Just keep dividing
the decimal number by 8 until results.
To convert from an octal number back to a decimal number, we
use the same procedure as we used to convert a binary number back
to a decimal number. In the binary conversion, a table showing
different powers of 2 was used. In the octal system, a table based on
the values of powers of 8, as might be expected, is used. Decimal-
octal equivalents are shown in Table 1-6.
HEXADECIMAL NUMBER SYSTEM
Hexadecimal ("hex") is another number system that is often
used with microcomputers. It is similar in value structure to the
8
469
5
2
7 —
-> 725
8
58
8
7
Fig. 1-1. Example of converting decimal number to the octal number system.
Table 1-6. Decimal/Octal Equivalents.
Decimal
Octal
Decimal
Octal
10
12
1
1
11
13
2
2
12
14
3
3
13
15
4
4
14
16
5
5
15
17
6
6
16
20
7
7
17
21
8
10
18
22
9
11
19
23
Decimal
Octal
20
24
21
25
22
26
23
27
24
30
25
31
26
32
27
33
28
34
29
35
octal number system, and allows easy conversion with the binary
number system.
As might be imagined, the base is 16 for the hexadecimal
system. The symbols are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E,
and F. In hex, A, B, C, D, E, F, are digits, not letters; that is, just as
the next digit after 8 (8 + 1) is 9, the next digit after 9 (9 + 1) is A,
the next digit (A + 1) is B, and so forth.
Conversion of binary numbers to hex is similar to converting
binary numbers to octal except that 4-bit groups are used instead.
The conversions are shown in Table 1-7.
You can convert from a decimal number to a hex number the
same way you did from a decimal number to an octal number, except
that you divide by 16 instead of 8. In converting from decimal to hex ,
it's recommended that you first convert the decimal number to
binary , and then convert the binary value to hexadecimal . Similarly ,
to convert from hexadecimal to decimal, first convert from hex to
binary and then go from binary to decimal.
To illustrate, to convert decimal 685 to hex, convert decimal
685 to binary, which will be 0010 1010 1101. Mark the numbers off
in groups of four bits from the right ; that is ,
10
2
1010
A
1101
D
and the result is 2AI) in hex.
BINARY CODES
Has the converting of decimal number to binary or binary
shorthand systems reminded you of anything? Sure, it's obviously a
form of code just like you see in the cloak and dagger films. The act
of conversion is called "coding" and codes and coding is what this
section is all about.
The decimal number system is easy to use because it has more
than likely been the system you have used most in your life. The
binary number system is less convenient to use because it is less
familiar, and few people can glance at a binary number and recognize
its decimal equivalent. You can readily calculate its value within a
few minutes, but you probably won't recognize it at a glance.
Therefore, the amount of time it takes to convert or recognize a
binary number quantity is a distinct disadvantage in working with
this code despite the numerous hardware advantages. Computer
designers have therefore come up with a special form of binary code
that is more compatible with the decimal system. This particular
code is known as binary coded decimal, which combines some of the
Table 1-7. Binary-
to-Hex Conversion.
Decimal
Hex
Binary
0000
1
1
0001
2
2
0010
3
3
0011
4
4
0100
5
5
0101
6
6
0110
7
7
0111
8
8
1000
9
9
1001
10
A
1010
11
B
1011
12
C
1100
13
D
1101
14
E
1110
15
F
1111
010
2
1011
B
011
3
(binary)
(hexadecimal)
10
Table 1-8. Standard 8421 BCD Code and the Decimal Equivalents.
Decimal
8421 BCD
Binary
0000
0000
1
0001
0001
2
0010
0010
3
0011
0011
4
0100
0100
5
0101
0101
6
0110
0110
7
0111
0111
8
1000
1000
9
1001
1001
10
0001 0000
1010
11
0001 0001
1011
12
0001 0010
1100
13
0001 0011
1101
14
0001 0100
1110
15
0001 0101
1111
characteristics of both the binary and decimal number systems.
In general, the BCD code is a system of representing the
decimal digits through 9 with a four-bit binary code, using the
standard 8421 position weighting system of the pure binary code.
The standard 8421 BCD code and the decimal equivalents are
shown in Table 1-8. Converting the BCD numbers into their deci-
mal equivalents is done by simply adding together the values of the
bit positions whereby the binary l's occur. Note, however, that
there are only ten possible valid 4-bit code arrangements . The 4-bit
binary numbers representing the decimal numbers 10 through 15
are invalid in the BCD system. To represent a decimal number in
BCD notation, substitute the appropriate 4-bit code for each deci-
mal digit.
One big advantage of the BCD code is that the ten BCD code
combinations are easy to remember once you have worked with
them a while. In fact, after some time spent in learning the BCD
code combinations, you should be able to make the conversion
almost as quickly as if the number were already in decimal form!
One big disadvantage of the BCD code is that it is less efficient
than the pure binary code because it takes more bits to represent a
given decimal number in BCD than it does using pure binary nota-
tion.
There are other codes used in microprocessors, but for now,
we will stop at pure binary and the BCD numbering system.
11
Chapter 2
Microcomputer Basics
A microcomputer is a very complex electronic device consisting of
thousands of microscopic transistors squeezed onto a tiny chip of
silicon, related leads, keyboard, housing, and other mechanical and
electronic components. Regardless of the type of microcomputer
used, the programmer should have a basic knowledge of how these
devices operate.
In general, there are two basic types of computers: digital and
analog. Digital computers represent everything in terms of digits.
That is, all data is discrete and discontinuous. There are some
hybrid computers that connect digital computers to analog comput-
ers , but most of today's computers are of the purely digital kind . You
should now be getting an idea of why certain number systems were
covered in Chapter 1.
An analog computer uses a quantity, such as an electrical
voltage, as an analog of some other quantity. For example, 3.145
volts in an electrical circuit might represent a velocity of 3,145 feet
per second in a ballistics simulation program . Analog computers are
fast for certain specialized applications, but they are not practical
for many purposes .
To help you understand the essential elements of a digital
computer, well-known analogy will be presented. Imagine a faith-
ful, loyal, dedicated employee, such as a secretary, who follows
every instruction to a "T." This secretary, given a manual of
procedures and some documents to work with , can refer to history
12
files and produce required reports for your company. He or she
needs only a calculator (to perform computations) and a sheet of
instructions. If he unerringly follows those instructions, he will
produce a stack of papers in his out-basket that represents a trans-
formed version of the information contained on papers in the in-
basket. If the secretary transforms legitimate inputs into correct
outputs by following the instruction sheet, those instructions can be
considered a correct and valid "program."
In the example above, the secretary performs five distinct
functions .
1. Reading source information (both the documents in the
in-basket, and the list of instructions).
2 . Storing intermediate results (remembers information for a
short time , either in her head or on a scratch pad) .
3. Computing, using a desk-top calculator (to find totals or to
arrange data into proper order) .
4. Writing transformed information (the required results in
the out-basket or records in files for future use) .
5. Controlling these activities (sequencing of these four ac-
tivities to achieve the required result).
Figure 2-1 shows that a computer can perform these five
functions, but all of the data and instructions must be supplied in a
special computer-readable form. In other words, the program is a
computer's equivalent of a manual of procedures. Under the guid-
ance of the steps in that program, the computer may read input data,
store intermediate results, perform arithmetic using numbers from
inputs and from previous computations, and write outputs in many
forms. The control element of the computer selects which of the
other four elements are to be used at any given time. The computer,
then, performs five functions similar to those performed by a sec-
retary:
SECRETARY
COMPUTER
Read
Input
Store
Storage
Compute
Arithmetic
Write
Output
Control
Control
As human beings, we perform input functions through our
senses: taste, smell, touch, sight, and hearing. Some computers
13
Documents
Keyboard
Instructions
(program)
Computer
Disk
Printed
reports
Tape unit
Teletypewriter
Files
Fig. 2-1 . A computer performs functions that are similar to those performed by a
secretary.
sense inputs by sight (optical character readers , for example) or feel
(wire contacts through holes in punched paper tape) . Some inputs
are simple electrical on-off signals from remote sources . Sound also
plays an important part in allowing computers to read.
Humans store information for short-term retention in their
memory, relying on a variety of filing systems for more permanent
storage. Computers also have memory. Their capacity to store
information varies from machine to machine, depending on the
number of external devices, such as tapes, disks, and drums, that
are used. The storage capacity of computers using these devices is
almost infinite.
Both man and his machines can perform arithmetic . The arith-
metic capability of digital computers ranges from elementary to
14
complex. As you learned in an earlier chapter, computers perform
all arithmetic operations using binary numbers . The computer can
also perform other "logical" functions such as determining whether
or not one number is greater than another.
We create output by our actions . We write , speak , or change a
situation appropriately. The computer produces output in the form
of rewritten magnetic tapes, disks, and drums; printed reports; and
even motor on/off controls. Since the computer operates electron-
ically, it can also control electronic circuitry, such as the circuitry
necessary to automatically open or close a flow valve in a water
supply system.
We can control both ourselves and our machines. Machines can
control only what they are instructed and permitted to control.
When the secretary does some work, he or she is responsible for
controlling the order in which various steps of the procedure are
performed. He can, under the guidance of the detailed instruction
list, read some information, perform some computations, and pro-
duce some output in the order specified in the program.
Computers are controlled by computer program's. The pro-
gram is a description of a detailed procedure that is to be followed.
Just as a theater program outlines the events that are to follow, a
computer program outlines the steps to be followed to arrive at a
solution to the problem presented. The program is interpreted by
the computer which turn various circuits on and off in the sequence
necessary to produce the solution.
COMPUTER STRUCTURE
The diagram in Fig. 2-2 shows the five basic elements of a
digital computer. Every digital computer, no matter how large or
small, has these five elements plus the set of instructions that tells
the computer what to do. A computer must be able to accept input
data, process it through arithmetic or logical operations, store some
intermediate results, and eventually produce output data— all under
the guidance of a central control element . The control element is
guided in its operations by the instructions supplied by a program-
mer. The five basic elements comprise the hardware of the com-
puter. Hardware can be touched, squeezed, observed; it is tangible.
The instructions, on the other hand, represent the software of a
computer. We may be able to observe, touch, or squeeze a storage
medium, but the specific bit patterns held within are not physical;
they are information.
Inputs: Nearly all computers require inputs from one or more
15
external sources . A computer that receives no input signals can only
repeat the same sequence of instructions over and over again . Some
small computers are used in precisely this way , but most computers
have inputs that can be brought into the computer for subsequent
processing.
To compute a payroll check, for example, the computer must
have the ability to fetch an employee record from a file and to read in
the number of hours worked in the week. These both require an
input path to the computer. In some simple applications where small
computers are used to replace older electromechanical logic , inputs
may not be required. A programmable controller of a numerically-
controlled milling machine may not require inputs. The program
contains the sequence of instructions which cause the machine to
mill the same part repeatedly . External inputs are of no value in this
case.
Inputs to the computer may take the form of punched cards,
magnetic tapes or disks, or simple switch closures. When a
keyboard is operated by a human, each key depression results in a
switch closure. The computer can accept this switch closure as a
binary signal and convert the key depression into a binary pattern.
i
Central
processing
unit (CPU)
1
1
Arithmetic-
logic unit
(ALU)
i
i
1
i
t
Input
i
Control
Output
k
w
9
■ ►
— »
i
►
t>
w
k
w
i
i.
4
1
Storage
(memory)
Fig. 2-2. Five elements in all digital computers.
16
That binary pattern, in turn, can be used to print a selected charac-
ter on a printer or display it on a cathode-ray tube (CRT).
Outputs: A computer must produce outputs to be useful. A
computer's output may be in the form of printed results, graphic
plots drawn with special plotting equipment, or simply an electrical
signal that can turn a lamp on or off. The range of possible outputs
from a computer is virtually unlimited. The output element of a
computer is selected when the control unit executes an instruction
that transfers data from the arithmetic-and-logic unit (ALU) storage
area, or when an input is to be output. Most often, the data comes
from storage, and was created by a complex combination of inputs
that were modified by the ALU.
The input and output devices are points at which humans
interact with the computer. Much care must be taken to make
computers easy for people to use, rather than making people adapt
to poorly designed or poorly programmed computers.
Storage: In most computer applications, data must be stored
before it is processed completely or used to produce outputs. The
electrical digital signals that represent the data values are placed in
the storage element, or memory. Instructions can also be read into
storage and held for future use.
Arithmetic: A computer processes information. That pro-
cessing is performed by the ALU which accepts data from input and
storage elements, and produces computed results for storage or
output. To add a pair of numbers, the ALU is directed to fetch the
values from storage, and to place the sum back into storage. The
ALU may include capabilities for addition , subtraction , comparison ,
logical operations, and even multiplication and division.
Control: All elements of a computer operate under the direc-
tion of the control element which opens and closes the various
pathways for data from input to storage, from storage to the ALU,
and from the ALU to output. The control element operates as
directed by the instructions provided in storage. By writing the
proper sequence of instructions, the computer programmer can
completely control the detailed transfers of data within the com-
puter to produce desired results. Thus, with different programs,
the computer can be made to perform different functions, even
though the underlying electronic circuitry remains unchanged.
SOFTWARE
Software consists of a collection of instructions that can be
followed by the control element of the computer. These instruc-
17
tions must be detailed step-by-step instructions. Unlike humans,
who can inject common sense into the completion of a task, a
computer is not capable of logical reasoning. A computer must be
ordered to do even the simplest part of a task. There are four major
classes of computer instructions:
1. Input/output instructions cause data to be accepted as
inputs, or to be produced as outputs.
2 . Arithmetic-logic instructions cause data to be transformed
through simple operations in the ALU. These operations
include addition, subtraction, shifting, and logical operations
(AND, OR, etc.).
3. Storage instructions move data between storage and other
elements.
4. Control instructions specify changes in the normal se-
quence of instruction execution.
The instruction set is the collection of general-purpose instruc-
tions available in a given computer. This set of instructions can
show you how that computer works. The number and type of
instructions are an indication of the ease with which the computer
can perform operations. Some computers, for example, have a
multiply instruction. Given two numbers, this instruction will pro-
duce the product. Most microcomputers, on the other hand, do not
have a multiply instruction. Multiplication can be done on these
computers, but many more instructions must be executed. Since
most microcomputers are used in applications that do not require
multiplication, the lack of a multiply instruction is seldom a prob-
lem. However, it is important to note that those facilities that are
not provided in the instruction set can be created through the
execution of the right sequence of simpler instructions.
INTERCONNECTION OF THE ELEMENTS
Each element of a computer can be treated as a subsystem.
Each element has certain inputs and outputs, and certain actions
that take place internally to transform those inputs into outputs. A
revised view of the five-block model of the computer is shown in
Fig. 2-3. Here, all of the inputs and outputs to each element of the
computer are identified. Note that except for the interfaces be-
18
ALU
u 'O
c c
o a
3 «
-J CC
LL 8)
< -o
Input
Output
selection
\v* selection
Input
4
Control
»
Output
w
in
\
7j
)
• ►
Input
*:
/"N
»• Output
data c
•=
c:
data
03 o
S
■c
to
u
CD
0)
CI)
tr 9s
cc
CO
Q
1
r i
r^
x/
T
Storage
Fig. 2-3. The interconnections between elements consist of both data and control
signals.
tween the computer and the outside world, the output from one
element becomes the input for another element. By analyzing how
these paths between elements operate, we can discover how a
computer functions in detail.
Most of the pathways for data are bidirectional. However,
issuing data to an input source , or attempting to acquire data from an
output destination is meaningless. These data pathways can be
easily limited to a single direction. On the other hand, data must
move in both directions between control and storage, and between
control and the ALU. Since data may flow both ways, these paths
are called bidirectional.
Notice that all of the control signals originate in the control
element, and that all data passes through the control element.
"Control" may be thought of as a gigantic switch-board that operates
at microsecond rates to switch data from one source to another
destination. In fact, this is precisely how contemporary computers
work.
At any one time, control may be directing one of the other four
elements to perform some operation. In very complex computers,
more than one element may be accessed at one time. The input
19
element of the computer has many possible data sources, but only
one of them is to be selected at a time. When reading from input
sources, the control element must first specify which input source
is to be selected. Control places some bit pattern on the wires that
comprise the input selection lines. The selected data is then placed
on the input data lines. Once input data has been acquired, the
control element must store that data somewhere for future use . The
data might be shipped off to the ALU , or to storage , or even to one of
the output destinations.
If the input data is to be saved in storage , the control element
must specify where in storage the data is to be placed. Since many
numbers can be stored, each one must be stored in a unique place so
each can be selectively retrieved. The data is placed on the data
lines, and the storage module is commanded to write (store) the
data. The command is sent by the control element through the
Read/Write selection line. The specific register into which the data
is to be stored is specified by a pattern of bits on the register
selection lines.
The specification of which input lines to read and into which
register to place the data in storage, is carried in an instruction.
That instruction contains three essential items of information:
1 . The operation to be performed (read data from an input and
store it away).
2. The source of the data (the specific input source to select) .
3. The destination of the data (the specific register into
which the data is to be placed).
One way to visualize this operation is to examine a small
sequence of instructions that might be found in a large program.
This brief instruction sequence (program segment) acquires two
input numbers and produces a sum which is output. This program is
summarized in the following sequence of instructions.
1. Accept a number from input source 5, and save that
number in storage at register 83.
2. Accept a number from input source 2, and save that
number in storage at register 43.
3. Read the first number (from register 83) and pass it to the
ALU, commanding the ALU to save that number.
4 . Read the other number (from register 43) and pass it to the
20
ALU, commanding the ALU to add it to the previously saved
number.
5. Accept the sum from the ALU and pass it to output desti-
nation 7.
Each of these instructions can be described in more detail by
referring to the signals that appear on the wires between the various
computer elements. For example, the first step above (accept a
number and place it in storage) can be described in more detail like
this:
1 . Control issues the number of the required input source (5)
on the input selection lines. The input element accepts that
number and selects that data source.
2. The data source presents some data (say, the number 113)
on the input data lines to control. Control accepts that number
and holds it temporarily.
3. Control issues the storage register number (83) to storage
by placing that number on the register selection lines. Con-
trol also commands the writing action on the Read/Write
selection line. Storage accepts the register number and gains
access to that register.
4. Control places the temporarily held data (113) on the data
lines. Storage writes that number into the selected register.
Obviously, such detailed English explanations could be dif-
ficult to follow for any reasonably complex set of instructions.
Therefore , a shorthand method is sometimes used to describe those
sequences. The narrative description for reading and storing a
number could be written in a briefer form like this:
1. Input selection control (5);
Input input selection (5)
2. Input data input (113, from source 5);
Temporary input data (113)
3. Register selection control (83);
Read/Write selection control (Write);
Storage register selection (83)
4. Data temporary (113);
Storage (at register 83) data
21
Each of the items named in this brief example is a register in
the computer. One of the control registers (which happens, in this
example, to contain the number 5) supplies its contents to the input
selection register.
Now, reconsider the application posed earlier: the production
of the sum of two numbers. In the following example, each of the
original instructions has been broken down into a number of detailed
steps. These steps are represented in the shorthand form. You
should fill in the descriptive shorthand for the last instruction
yourself to be certain that you understand exactly how the computer
works :
1. Input selection control (5);
Input input selection
Input data input (113);
Temporary input data
Register selection control (83);
Read/Write selection control (Write);
Storage register selection
Data temporary;
Storage register 83 data (113)
2. Input selection control (2);
Input input selection
Input data input (102)
Temporary input data
Register selection control (43);
Read/Write selection control (Write);
Storage register selection
Data temporary;
Storage register 43 data (102)
3. Register selection control (83);
Read/Write selection control (Read);
Storage register selection
Data storage (113);
Temporary data
Function selection control (Save);
ALU data temporary (113)
4. Register selection control (43);
Read/Write selection control (Read);
22
Storage register selection
Data storage (102);
Temporary data
Function selection control (Add);
ALU data temporary (102)
Function selection (Fetch);
Temporary
Output selection ( );
output selection
Output (215)
SCALING OF COMPUTERS
It might appear that the size of numbers is limited by the widths
(number of data lines) of the data paths that exist between elements .
Actually, in the example, data path widths of eight bits would be
sufficient, since the numbers never got larger than 215 (an 8-bit
register can hold numbers up to decimal 255). However, even
larger numbers can be handled by breaking them up into pieces.
Then each part of the number has to be handled independently, and
that would require more instructions.
Large computers have wide data paths; smaller computers
have narrower paths. Some of the largest computers have paths as
wide as 64 bits for numbers. Programmers seldom have to resort to
the slow technique of breaking a number up into pieces and pro-
cessing each piece separately. On the other hand, a small micro-
processor may have paths as narrow as four bits. Processing a 64-bit
number would take at least 16 times as long as it would take on the
larger data path.
There are special electronics techniques that can be used with
large computers to make them operate much, much faster. How-
ever, because these techniques are only economical with very large
computers, they are seldom used with microprocessors. Some of
the largest computers can execute instructions 400 times faster
than a typical microprocessor. That speed advantage, multiplied by
the speed advantage of wide data paths, marks the difference be-
tween large, medium, and small computers.
Large-scale computers, or supercomputers, have thousands of
ICs and require huge rooms for installation. Purchasing one hour of
computer time may cost more than $3000. The only way these fast,
powerful computers can be economical is to have a large number of
23
users. Each user occupies only a small percentage of the computer
resources, and for only a short period of time.
These large computers have large input/output systems with
millions (or even trillions) of bits of storage on magnetic tapes and
disks . The main storage module of the computer may have over one
million registers, and the ALU-control element may be designed to
permit hundreds of people to use the computer simultaneously.
Most of these people use supercomputers to solve mathematical
and engineering problems. These kinds of computers are seldom
used for commercial data processing.
Commercial data processing is most often done on a computer
scaled to the size of the business. For example, large insurance
firms use complex medium-scale computers. Accessing information
about policies and billing data requires a large input/output capac-
ity, but the need for processing is relatively small. However, a
relatively large computer is required to support hundreds of com-
puter terminals in agents' offices throughout the country.
A typical medium-scale computer might have disk and tape
storage that rivals that are used with a supercomputer for capacity.
However, the central processing unit (CPU) will seldom be as large
or complex, and storage may be limited to 250,000 registers or so.
An hour of computer time on such a system might cost $800. By
using Vn of the computer's capacity for three minutes, a business
executive can perform all the computations required for a small
office at a cost of about $10.
Small-scale computers are usually called minicomputers.
Some minicomputers are used in small- to medium-sized organiza-
tions for business data processing . However, more of them are used
to perform communication chores for a larger computer. The
minicomputer may service hundreds of telephone lines on the
"front-end" of the computer, passing data to the central medium-
sized computer over a set of highspeed wires . Other minicomputers
are used to effect on-line control of production processes.
A typical minicomputer might have 65,000 registers of main
storage, and a relatively simple ALU-control element. Some appli-
cations might demand disk or tape storage , but many do not . The
operating cost of a minicomputer might be as low as $40.00 an hour .
By occupying the entire computer for 15 minutes, an engineer may
be able to control an experimental process at a cost of about $10.
The least expensive computers are microcomputers . Some of
these are used in small businesses as data processing tools; others
24
are used for personal entertainment; and still others are installed
inside other equipment for internal control . These computers are so
inexpensive that dedicating one to a single application is feasible. A
small retail establishment might use a microcomputer with disk
storage, 16,000 bytes registers of main storage, and a simple
ALU-control element. The cost of operating such a microcomputer
system might be as low as $10 a day. By having the entire computer
available at all times, the retailer may be able to better control store
operations at a cost of about $10 a day.
Technologically, all of these computer alternatives are alike
except for their underlying capacity. The lower capacity computers
cost less , but take longer to perform their tasks . Finding an account
balance for a customer in a bank might require 1/10,000 of a second
on a large supercomputer and two seconds on a microcomputer.
Will the customer notice? Is the faster speed necessary, especially
in view of the fact that the teller's terminal may require 20 seconds
to print out the account information? In other words, for many
applications, time is not a critical issue, and a less expensive
computer can be used.
MICROPROCESSORS
When the CPU (the ALU and the control element) of a com-
puter is implemented in a single integrated circuit (IC), we call that
the central processor a microprocessor. The term microprocessor is a
contraction of microelectronics and central processor, and indicates
the technology used in the heart of the computer.
A microprocessor is not an entire computer: it is only the ALU
and the control portion of a computer. When the microprocessor is
combined with storage, and input/output devices, however, the
result may be properly called a microcomputer. A microcomputer is
any computer based on a microprocessor.
At this point, it is important to distinguish between two dif-
ferent kinds of microcomputers. One kind integrates all computer
elements on one IC or on a very small number of ICs. A "one-chip
microcomputer" cannot be distinguished from its microprocessor
counterpart by simple inspection. However, one-chip microcom-
puters are small, powerful computers that are useful for a wide
range of special applications. They are found in consumer goods,
electronic games, and electronic interfaces between larger
computers and peripheral devices like cassette tape drives.
One-chip microcomputers are inexpensive, but limited. They
25
are useful in certain low-cost applications that demand little in the
way of computing power or storage capacity . However, because the
pins of the IC are devoted to input and output wires, these devices
have little expansion capability.
The more popular kind of microcomputer is made up of sepa-
rate ICs for the CPU, storage, input, and output. All these elements
are interconnected by wiring etched on a printed circuit board.
When a microcomputer is created out of many individual elements,
as are many of the popular single-board computers, more power is
available to the user. If the application demands more memory,
more memory boards can be added to the configuration. If special
I/O capabilities are required, they can be installed as special
boards . Although more expensive than the one-chip microcomput-
ers , microcomputers in printed circuit board form may be used in
vastly more complex configurations, and may contain an almost
limitless variety of storage and I/O capabilities.
Many of the general-purpose single-board computers use many
one-chip microcomputers to act as I/O interfaces. A single com-
puter complex might have dozens of one-chip microcomputers per-
forming peripheral interface chores under internal software
control— all supporting a single fast microprocessor with a large
amount of storge on other boards . More and more interface systems
are composed of one-chip microcomputers that have been suitably
programmed. Most of these can be treated, however, as dedicated
ICs. Internally, they've been programmed to perform some specific
task. However, since the user or maintenance technician cannot
change any of that programming, the programmed one-chip mi-
crocomputer is effectively a special-purpose IC developed for the
intended interface application. The trend is away from huge cen-
tralized computer systems to systems of computers in which the
computing power is distributed among many small one-chip mi-
crocomputers.
COMPUTER BUS SYSTEMS
A computer bus can be defined as a group of wires that allow
storage, control, and I/O devices to exchange information. One of
the best ways to achieve high-speed operation in a computer is to
keep all of the buses or pathways between various computer ele-
ments separated. In addition to the pathways to and from control as
shown in Fig. 2-3, very fast computers include special pathways
between other elements. A special circuit path called direct mem-
ory access (DMA) may exist between input and storage elements so
26
that data can be sent rapidly to storage while other operations are
being performed. The more complex the computer, the more likely
it is to have some special interelement paths. However, most
microcomputers are designed with only simple pathways. Effi-
ciency is sacrificed for the simplicity of a more organized structure .
Master Bus Control
The bus system can be used to transfer information between a
master (controlling) and a slave (controlled) element of the com-
puter. The design of the master element, normally what has been
previously referred to as "control ," defines the order, arrangement,
and timing of the various electrical signals that affect information
transfer. All slave elements must comply with the rules laid down
by the master element.
Data is always transferred between one of the slaves and the
master that is in control of the bus system. Since there is only one
address (or location) on the address bus (shown in Fig. 2-3 as the
"register selection" pathway) at a time, only a source or a destina-
tion register can be specified. One of the bits on the control bus (the
path linking control to storage labelled "Read/Write selection" in
Fig. 2-3) specifies whether the master is the source (and, hence , the
slave is the destination) or the destination (in which case data is
being read from the slave) . Of course , with two separate address
buses, data could be transferred directly between two slaves under
master element control. However, the improvements in informa-
tion transfer rates that can be obtained by having more than one
address bus are generally not worth the effort on small computers.
Such multi-bus systems are found on large computer systems where
speed is paramount.
The Control Bus
The key to understanding a computer is to examine its control
bus. The address and data buses of a computer may be wider, but
the control bus is always the most complex of the three. The
address bus is always used to select one particular register to be
involved in a transfer to or from the microprocessor. The data bus is
always used to transfer data. But the control bus is composed of
many different kinds of signals, all of which complex interpretations
over time .
Writing to Storage
Writing or storing data takes place in a fashion analogous to
27
reading or retrieving data. The data is put on the data bus by the
CPU. (For those who are curious, Fig. 2-4 shows a detailed view of
the address bus. VMA and /W (low) signals are produced just like
the equivalent signals used during reading.) However, the storage
element cannot take the data from the data bus until the specific
register has been addressed. It takes time to gain access to the
required register. This is called the access time. (In most comput-
ers with a sequence of this kind, the storage element would cause
writing to occur at the instant the E signal made the end-of-cycle
high-to-low transition.)
Transferring data from one storage register to another simply
requires two successive read-and- write storage cycles. Some in-
structions in the computer cause successive cycles like this to
happen automatically. Invariably, however, the process ends with
another storage read operation which will retrieve another instruc-
tion from the program that is in memory for execution.
Master Clocks
To create the enable (preparation) signal for controlling the
One bus cycle
, 1000 ns
1
o~— 1 f
Address 1
bus k\\\\\ l
VMA j- \\\V\\\|
R/W } AWWWI
is
(Write cycle) ^^
° a l a r v\\\\\tv 2 \\ n \\^w! iss
bus
1 -
Data
from
LEGEND CPU
_ Hi9h
Low
J:-| r
•j changing
- ^ -1& Data may
be high or
low, but
stable
Fig. 2-4. A typical timing diagram for a write to storage.
28
1k
+5 — VvV-
^o
1k
+5 — WV-
■^o-
1k
+5 — VW-
^"o
1k
+5 — \W-
-<So
t
1k
+5 — wv-
^
t:
1k
+5-A/W-
^c-
1k
+5 — WV
D-
-0^
1k
+5 — vw-
f>
-c^o
Input
£
-►D7
-*D6
■>D5
>D4
-►D3
-*D2
-*D1
>D0
-A15
-A14
-VMA
■R/W
Fig. 2-5. A simple input port places the input data on the data bus only when
addressed for reading with a valid memory address.
bus cycle, a central clock is required for the microprocessor, or for a
part of the microprocessor IC. In either event, an external
frequency-determining component is necessary.
Storage and the Buses
The signals on the address and control buses, and on the data
bus during writing are all produced directly by the microprocessor.
29
Sometimes there may be digital logic external to the microproces-
sor itself required to create all of these signals, but these external
ICs are considered part of the microprocessor complex. How these
signals are used determines the complexity of the input, output, and
storage elements of the microcomputer.
TYPES OF STORAGE
Storage in a microcomputer is usually made up of read-only
memory (ROM) ICs for permanent storage, and random-access
memory (RAM) ICs for temporary storage. The ROMs are written
once before installation in the microcomputer. Since these storage
elements are not written to by the microprocessor, they can be
permanently encoded with a program, and that program will be
ready to execute whenever power is turned on. On the other hand,
the RAM uses semiconductor ICs that can be both read and written
to. However, when power is first applied their initial data contents
are random. Data cannot be stored in semiconductor RAMs while
the power is off .
BUS CONTROL OF I/O
Input signals can be connected to the data bus for use when the
instructions call for the reading of input data . A simplified version of
the techniques used for storage shown in Fig. 2-5 can be used. The
address bus and parts of the control bus are combined to create an
input signal. When that signal is high, the input data is sent to the
data bus lines.
30
Chapter 3
Computer Arithmetic
In Chapter 1 of this book you were introduced to how to use the
binary number system, how to convert decimal numbers to binary
numbers (and vice versa), and how to convert between other
number systems. This chapter is designed to introduce you to the
fundamentals of binary mathematics— addition, subtraction, mul-
tiplication, and division. Since microprocessors use binary numbers
for data and control, it is extremely important that you become
familiar with them.
ADDITION AND SUBTRACTION OF BINARY NUMBERS
Binary numbers can be added and subtracted in much the same
way that the more familiar decimal numbers are. When doing binary
arithmetic, remember that when you add or subtract two binary
numbers , the result must be equal to the value obtained by adding or
subtracting the decimal equivalents and then converting that result
to a binary number.
It is obvious that we could add two binary numbers by con-
verting the binary numbers into their decimal equivalents, adding
the decimal numbers as we did in grade school , and then converting
the result back into the binary numbers. However, there's an easier
way. Perhaps you won't think it's easier at first, but after you
become more familiar with the binary number system, you will find
it so.
31
In the binary system, there are four rules that help to make
addition quite simple. They are summarized as follows:
1. + =
2. + 1 = 1
3. 1 + 1 = with a carry of 1 equals 10
4. 1 + 1 + 1 = 1 with a carry of 1 equals 11
Before continuing, let's review the decimal/binary equivalents
shown in Table 3-1.
With the above table in mind, let's look at the following addi-
tion problem.
1010
+101
1111
Looking at the conversion table, we see that binary number 1111 2 is
equal to decimal number 15. Now let's add these numbers another
way . Again , looking at the table , we note that the top number ,1010,
is equal to the decimal number 10; the lower number, 101, is equal
to the decimal number 5. So, the problem states 10 + 5 = 15. Now
the total should be converted to a binary number. The table tells us
that decimal 1 5 i s equal to binary 1 1 1 1 — our original answer . So we
know our addition was correct.
A more complicated example of binary addition, with several
carries, is shown as follows:
11111
+1111
101110
At first glance you might have thought the sum of the two numbers
in the example above should have been 12222, but you must re-
member that we are working with the binary number system, and
our only digits are and 1 . We must go back to the four rules given
earlier in this chapter. Starting with the first column at the right, we
add binary 1 to binary 1 (Rule #3) . The result is a which is written
under the first column, and a 1 that must be carried to the second
column . In the second column , 1 plus 1 equals with a carry of 1 . To
this sum, you must add the 1 you carried from the first column.
Thus, plus 1 (Rule #2) equals 1; this result is written under the
32
Table 3-1. Decimal-
Binary Equivalents.
DECIMAL
BINARY
1
1
2
10
3
11
4
100
5
101
6
110
7
111
8
1000
9
1001
10
1010
11
1011
12
1100
13
1101
14
1110
15
1111
16
10000
second column sum. In column 3, 1 plus"l equals with a carry of 1.
To this sum, the second column carry is added. This yields a third
column sum of 1 (0 plus 1 = 1). Rules 2 and 3 are used to obtain the
sum in this column. In column 4, 1 plus 1 equals with a carry of 1.
To this sum, the third column carry is added, yielding a fourth
column sum of 1 (0 plus 1 = 1). Now we have only the carry to add to
the number in column 5, which gives us 10 as the sum in the fifth
column. This figure was obtained by using rule #3 (1 + 1 = with a
carry of 1). The carry is written immediately because there are no
more columns to carry it to.
If we write the equivalent decimal numbers, we'll find that
11111 in binary is equal to decimal 31, and 1111 in binary is equal to
decimal 15. The sum of these two decimal numbers is 46. Decimal
46 is equal to binary 101110, proving that our binary addition is
correct.
Binary addition is not limited to two figures. On the contrary,
any number of figures may be added as long as the basic rules are
followed. Here they are one more time.
1
= 10 (zero with carry of 1)
+ 1 = 11 (one with carry of 1)
Now let's try adding three binary figures just to see how this is
accomplished. Look at the following figures.
33
110101
11011
+ 101111
1111111
To add these three binary numbers, start at the extreme right
as before and add the first column . We have 1 + 1 which equals zero
(with a carry of one) plus 1 which equals 1 (1 + 1 = 0; + 1 = 1 with
a carry of 1 to the second column) . Adding this carried 1 to (the top
digit in the second column), gives us 1 (Rule #2). This 1 added to
the remaining two Is in the column gives us 1 with a carry of 1 (Rule
#4). In the third column, the carried 1 plus the top 1 in the column
equals with a carry of 1 ; plus (the second digit from the top)
equals 0; then plus 1 equals 1 (Rule #2) . Thus the digit 1 is written
for the sum of the third column and we have a carry of 1 .
This procedure is continued until we have a total sum of
1111111 in binary. To check this addition, convert the binary num-
bers to decimal numbers. They are, from top to bottom, 53, 27, and
47 respectively. These three decimal numbers added together
gives a sum of 127. The decimal number 127 is equal to the binary
number 1111111. So our addition is correct.
In performing binary addition, do not use a pocket calculator as
this will only confuse you. Also, you might find it helpful to make a
small pencil mark at the top of the column to indicate each 1 carried.
The carries of our last example could be indicated as follows:
11111
110101
11011
+ 101111
1111111
You may not need these marks in simple binary addition, but in
the more complex problems you'll certainly find a need for them.
For example, let's look at the following addition of four binary
numbers.
11001
10101
11101
+ 10101
The addition is done, and the carries are marked as follows:
34
1 111 11 11 1 11
110 1
10 10 1
1110 1
+ 10 10 1
110
To add these figures, first deal with the column on the extreme right
as discussed previously; we have 1 plus 1 equals with a carry of 1.
A small 1 is then placed above the second column before we proceed
to add the rest to the first column. We have another 1 plus 1 which
again gives us plus another 1 to carry . So a second small 1 is placed
above the second column as shown in the example above. The total
of the first column is therefore 0.
In the second column, we have four zeros which would total 0;
then the two l's (from our carries) are added . Since 1 plus 1 equals
with a 1 to carry , is written as the sum of the second column , and a
small 1 is placed at the top of the third column.
When the third column is added in the same manner, the sum is
with two l's to carry . The sum of the fourth column is also with a
carry of two l's. When we add the fifth column, we have 1 + 1, which
equals and with 1 to carry, so we place a 1 over the sixth column's
place . We add the next 1 plus 1 which gives another 1 to be placed in
the sixth column. Now we have to add the two carries, which gives
us a under the fifth column and a third 1 to carry to the sixth
column.
In the sixth column, there are no numbers to be added— just
the numbers that have been carried. One plus 1 equals with a 1 to
be carried to the seventh column; we place a small 1 where the
seventh column would be. Now we have a plus the third 1 that we
carried to add. That gives us the sum of 1 for the sixth column.
The seventh column has only a single carry so it is written
down at the bottom as the seventh figure in the total sum. This gives
us a binary sum of 1100000.
The decimal equivalents of the binary numbers just discussed
are as follows:
25
21
29
+ 21
96
35
Subtraction
Binary subtraction is performed exactly as decimal subtraction
is performed, so a review of decimal subtraction is in order. You
know, for example, that if decimal 1827 is subtracted from 6845, the
difference obtained is 5018.
6845 Minuend
- 1827 Subtrahend
5018 Difference
In the right-hand column, the digit 7 is larger than the digit 5 in the
minuend, so a 1 is borrowed from the next higher-order digit in the
minuend (the 4 in our case). The 5 in the minuend becomes 15 and
the 4 becomes 3. No other borrowing is necessary in our example.
When subtracting binary numbers there are a few basic rules to
remember.
1. - =
2. 1 - 1 =
3. 1 - = 1
These are three of the four subtractions you will have to
perform in binary . The other is to subtract 1 from 0. In this case, you
must borrow from the next digit to the left as you would in decimal
subtraction. Thus the fourth rule is:
10 - 1 = 1
With these basic rules in mind, let's work a few examples.
11011
-1001
10010
Starting from the right-hand column ,1-1=0 (Rule #2) in the first
column; 1-0 = 1 (Rule #3) in the second column; 0-0 = (Rule
#1) in the third column; 1-1 = (Rule #2) in the fourth column;
and in the last column, 1 - = 1 as stated in Rule #3.
The subtraction may be checked by doing the same problem
using decimal numbers. Binary 11011 is equal to 27 in decimal and
binary 1001 is equal to decimal 9. Therefore, 27 - 9 = 18. When you
convert decimal 18 to binary, you'll find that the number is 10010,
the same as our original answer. Our subtraction was correct!
You may also check binary subtraction by adding; using binary
addition. In our previous example, we found the difference to be
36
10010 in binary. If we add this to 1001, we get an answer of 11011,
again proving our subtraction correct.
Now let's look at another example which requires borrowing.
101101
-11011
10010
The first column is regular subtraction, but in the second column it
becomes necessary to borrow 1 from the third column. The differ-
ence for the second column will then be 1 since 10 - 1 = 1. Since the
1 in the third column was transferred to the second column during
the borrowing, the third column subtraction is - = 0. One from
one in the fourth column is again (Rule #2) . The fifth column again
requires borrowing. The 1 is borrowed from the sixth column,
making the problem 10 - 1 = 1 and completing our subtraction.
The subtraction in the preceding problem was really not too
difficult since all borrowing involved adjacent columns. In the fol-
lowing problem, however, we must borrow from the third column,
making the value in the second column 10. From the binary 10 we
have in the second column, we borrow 1, giving us 10 in the first
column and leaving 1 in the second column . The rest of the problem
now becomes simple subtraction.
11100
-1001
10011
MULTIPLICATION AND DIVISION OF BINARY NUMBERS
Multiplication is a short method of adding a number to itself the
number of times specified by the multiplier. Binary multiplication
follows the same general principles as decimal multiplication.
However, with only two possible multipliers (1 or 0), binary mul-
tiplication is much simpler than decimal multiplication. As with
binary addition and subtraction, there are a few simple rules to
follow when multiplying binary numbers.
1. x =
2. x 1 =
3. 1 x =
4. 1 x 1 = 1
37
As in addition and subtraction, once the multiplication is performed
in binary, the answer may be checked by converting all numbers to
their decimal equivalents and doing the problem again.
Let's multiply the binary number 1010 by binary 11; the
problem is written as follows:
1010 Multiplicand
xll Multiplier
1010
1010
11110 Product
To multiply , we use the right-hand digit in the multiplier to multiply
each digit in the multiplicand. So, using the four basic rules as a
guide, 1x0 = 0, 1x1 = 1,1x0 = 0, and 1x1 = 1 or 1010. The
second 1 in the multiplier is used to multiply each digit in the
multiplicand again, just as in decimal multiplication. All that's left to
do now is to add using the rules we learned earlier. Our answer is
11110.
Binary multiplication becomes somewhat more difficult when
we have to do a series of carries. For example, let's multiply the
following binary numbers:
1110
x 111
In this example, the multiplication is standard, but the addition of
the three subproducts is complicated by carries. To illustrate,
1110
x 111
1110
1110
1110
1100010
Using the four rules of binary addition, the first is merely brought
down . In the second column , 1 + = 1 . In the third column , 1 + 1 =
with a carry of 1 . In the fourth column, 1 + 1 = with a carry of 1;
then 1 plus the 1 carried from the third column = with another
carry of 1. In the fifth column, 1 + 1=0 with a carry of 1. Then,
adding the two l's carried from the fourth column, we get with
38
another carry of one. In the sixth column, 1 + 1 + 1 equals 1 with a
carry of 1 (or 11 since there are no other digits to add in the seventh
column). The answer, therefore, is 1100010.
If the process seems difficult to you at first, practice several
problems with carries, and then check your answer by converting
.the problems to the decimal number system. If any problem does
not work out correctly, be sure to repeat it until you locate your
mistake.
Binary Division
Division is the reverse of multiplication. Therefore, since
multiplication primarily involves addition, division primarily in-
volves subtraction. If you learned the basic principles of binary
subtraction earlier in this chapter, you should have little trouble
doing binary division.
The numbers in binary division are set up in much the same
way as decimal numbers are set up in conventional decimal division .
For example, in dividing binary 100 into binary 1000, the problem is
set up as follows:
100/TOOO
In the above example, the divisor is 100 and the first three digits in
the dividend are 100, so 100 will go into these three digits once.
Then the divisor is multiplied by this 1 and the results written
beneath the first three digits. Now we subtract. The remaining is
brought down. The divisor (100) will go into zero times, so we
place a in the quotient for a total of 10.
10
100/TOOO"
100
00
Now look at the following example. Here 101 is divided into
1111.
11
ioi Jim
101
101
101
39
Binary 101 goes into binary 111 once , so we place a 1 above the third
1 from the left. Then we subtract 101 from 111 leaving 10. The
remaining 1 in the dividend is brought down and the divisor (101)
goes into this 1 time with no remainder. Thus, the result of this
division is binary 11.
The preceding examples were relatively short and quite sim-
ple, but they should suffice to introduce you to binary division. In
longer problems , the division is essentially the same . There may be
many more steps and more chances to make errors, but the division
is done the same way . It is important to do your borrowing when you
subtract . When you borrow 1 from 1 , for example , you get binary 10
and leave behind. If you borrow 1 from 10, you get 10, and leave 1
behind. To remind yourself that you have borrowed, put the appro-
priate figure near the original digit . If you don't do this , chances are
that you will forget what the digit should be and make a mistake.
Learning binary arithmetic is mostly a matter of getting prac-
tice, so do several problems daily until the procedure becomes
second nature to you . Always convert the binary numbers to deci-
mal ones and check your math for errors. If any are found, rework
the problem until you find your mistakes.
FRACTIONS AND DECIMALS
Converting decimal fractions and decimals to their binary
equivalents is not quite as easy as converting whole numbers. The
value of the negative powers of 2 decreases as the exponent in-
creases, whereas the positive powers of 2 are just the opposite.
Nevertheless, fractions and decimals can be converted to their
binary equivalents.
In some cases, just like within the decimal system, an exact
equivalent cannot be obtained. Take, for example the decimal frac-
tion Vs; it equals .333... and no matter how far we carry this
expression, it will never work out evenly. While it's true that the
more 3's that are added to the right of the decimal point, the more
accurate the decimal expression of the fraction becomes, we will
never get an exact equivalent of the fraction Vz. The inability to
convert some fractions to an exact "decimal" equivalent should be
no problem in either the binary or decimal number systems. The
decimal equivalent can simply contain a sufficient number of digits
to give the particular degree of accuracy needed.
A complete table showing the negative powers of 2 up to 2" 10 is
given in Table 3-2. Note that as the negative exponent increases,
the value of the fraction and the decimal equivalent decreases.
40
Table 3-2
. Negative Powers of 2.
2- 1 =
1
2
=
0.5
2" 2 =
1
4
=
0.25
2- 3 =
1
=
0.125
2" 4 =
1
16
=
0.0625
2" 5 =
1
32
=
0.03125
2" 6 =
1
64
=
0.015625
2" 7 =
1
128
=
0.0078125
2" 8 =
1
256
=
0.00390625
2" 9 =
1
512
=
0.001953125
O-10 _
1
1024
=
0.0009765625
Table 3-3 gives the binary equivalents of a set of fractions (six-
teenths). You can see that we work with fractional binary numbers
in essentially the same way as we do with whole numbers . As we
work from the binary point to the left in whole binary numbers , the
value increases. As we go from the binary point to the right in
fractional binary numbers, the value of each term decreases.
The addition and subtraction of binary fractions is done in the
same way as the addition and subtraction of whole binary numbers.
Carrying and borrowing procedures are the same, even across the
binary point.
When adding mixed binary numbers and whole binary num-
bers, be sure to line up the binary points and to add the columns one
at a time.
The problems of multiplying and dividing binary fractional
numbers are essentially the same as those encountered when
working with our regular decimal numbering system. Division
problems are handled the same way as decimal divisions: when
41
1
16
= 0.0625
= 0.001
1
8
= 0.125
= 0.0010
3
16
= 0.1875
= 0.0011
1
4
= 0.250
= 0.0100
5
16
= 0.3125
= 0.0101
3
8
= 0.375
= 0.0110
7
16
= 0.4375
= 0.0111
1
2
= 0.500
= 0.1000
9
16
= 0.5625
= 0.1001
_5_
8
= 0.625
= 0.1010
11
16
= 0.6875
= 0.1011
3
4
= 0.750
= 0.1100
13
16
= 0.8125
= 0.1101
7
8
= 0.875
= 0.1110
15
16
= 0.9375
= 0.1111
_16
16
= 1.000
= 1.0000
Table 3-3. Binary
Equivalents of Fractions in Sixteenths.
dividing with a decimal number, get rid of the decimal in the divisor
by moving the decimal point to the right in both the divisor and the
dividend. In other words, you have the same basic problem in both
number systems— keeping track of the decimal point. Here are
some examples of binary multiplication and division.
42
10.1
10.1
10.1
101
110.01
0.01/0.0001
0.01
o
43
Chapter 4
Boolean Operations
Along with the basic mathematical processes examined earlier, the
microprocessor in the ATARI 800 can manipulate binary numbers
logically. This system was conceived using the theorems developed
by the English mathematician George Boole (1815-1864). Boolean
values are used in the process of reasoning (Boolean algebra), or in
a deductive system of theorems using a symbolic logic, and dealing
with classes, propositions, or on-off circuit elements. Boolean
algebra employs symbols to represent operations such as AND,
OR, NOT, EXCEPT, and in some cases (in programming) if ...then
to permit mathematical calculation.
The simplest kind of Boolean expression states a relationship
which may or may not be true, between two quantities. If the
quantities are numeric, then the possible relations are strict in-
equalities; <, >; and reflexive inequalities: less than or equal,
< =, and greater than or equal, > =, equals, =; and does not equal,
^. If the quantities are non-numeric, for instance, the address of
apartments, it makes no sense to talk about inequalities which
derive from an ordering of values, but the relationships "equals" and
"does not equal" are still meaningful.
A relational expression results in a Boolean value, 1 or 0,
depending on whether the two quantities compared in the relational
expression do or do not satisfy the given relation. If variables or
numerical expressions are written to represent the related quan-
tities , the values of these variables or expressions are first obtained
44
and then examined to determine whether or not the indicated
relationship holds for these values.
Relational expressions are the most obvious , but they are not
the only kind of Boolean expression. We sometimes wish to base a
decision on whether or not several relational conditions hold
simultaneously or on whether or not at least one of several possible
conditions hold. Consider the following:
The U.S. Postal service has recently imposed restrictions on
the maximum size and weight of a package to be sent by parcel post.
The weight must not exceed 44 pounds , and the sum of the length
plus the girth must not exceed 72 inches. Assume that for parcels of
rectangular cross-section, the dimensions are given as values of the
variables A, B, and C in units of inches, and the weight as the value
of WGHT in pounds. However, the dimensions are not necessarily
given in order from greatest to least. We must write a procedure to
determine whether or not any given parcel is acceptable .
In order to calculate the postal dimension, we need to know
which of the three dimensions is the largest, for the equation
restricts girth more than it does length . We can compute a value for
the postal dimension by making use of conditional assignment.
IFA = B&A = C THEN
POSTALDIMENSIONS = A + 2*(B+C);
ELSE IF B = C THEN
POSTALDIMENSION = B + 2*(A+C)
ELSE
POSTALDIMENSION = C + 2*(A+B);
We won't take time to investigate the entire program; rather,
let's look at the first line of the statement. Here two conditions are
tested to find out whether A is the largest of the three dimensions . If
it is, then the expression A + 2*(B+C) is evaluated and assigned to
the variable. Otherwise, if one or the other of the conditions tested
in the first line is false, the assignment on the second line is not
evaluated, but instead control passes beyond the first ELSE. The
second alternative is tried only after it has been determined that A
cannot be the largest of the three dimensions, etc.
BOOLEAN ALGEBRA
Before going further into conditional execution, the reader
should have a good knowledge of Boolean Algebra. This will help
him or her to approach the work more intelligently.
45
In the spring of 1847, George Boole wrote a pamphlet entitled
"A Mathematical Analysis of Logic." Later, in 1854, he wrote a
more exhaustive treatise on this subject which was entitled. "An
Investigation of the Laws of Thought." It is this later work which
forms the basis for our present day mathematical theories used for
the analysis of logical processes.
Although conceived in the 18th Century, little practical appli-
cation was found for Boolean algebra until 1938 when it was found
that Boolean algebra could be adapted for the analysis of telephone
relay and switching circuits . Since that time , the extent of its use
has expanded rapidly, roughly paralleling the development and use
of more complex switching circuits such as those found in present
day automatic telephone dialing systems and digital computers.
Thus Boolean algebra has become an important subject which must
be learned if the operation of digital computers and other devices
using complex switching circuits is to be understood.
CLASSES AND ELEMENTS
In our universe, it is logical to visualize two divisions; all
things of interest in a discussion are in one division and all things
which are not of interest in the discussion are in the other division.
These two divisions comprise a set or class which is designated the
universal class, and all things contained in the universal class are
called elements. One may also visualize another set or class; this
class contains no elements and has been designated the null class.
In a particular discussion, certain elements of the universal
class may be grouped together to form combinations which are
known as classes. However, these classes are actually subclasses
of the universal class and thus should not be confused with the
universal class or the null class. Each subclass of the universal class
is dependent on its elements and the possible states (stable, unsta-
ble, or both) that these elements may take.
Boolean algebra is limited to the use of elements which have
only two possible states, both of which are stable. These states are
usually designated TRUE (1) or FALSE (0) . Thus , to determine the
number of classes (or possible combinations of elements) in
Boolean Algebra, we find the numerical value of 2" when n equals
the number of elements . If we have two elements (each element has
two possible states), we have 2 2 possible classes. If the elements
are designated A and B , then A may be true or false and B may be
true or false. Using the connective word "and," the classes which
could be formed are as follows:
46
A true and B false
A true and B true
A false and B true
A false and B false
However, if the connective word "or" is used, four additional
classes are formed. The differences between the two classes,
groups or forms are discussed below.
VENN DIAGRAMS
The Venn diagram is a topographical picture of logic, com-
posed of the universal class divided into classes depending on the
number of elements. Venn diagrams may be used to illustrate
Boolean logic as follows:
Consider the universal class as containing submarines and
atomic-powered items. Let A equal submarines and B equal
atomic-powered items. We have four classes which are:
(1) Submarines and not atomic powered
(2) Submarines and atomic powered
(3) Atomic powered and not submarines
(4) Not submarines and not atomic powered
These four classes are called minterms since they represent
the four minimum classes of elements . The opposite of the min-
terms are the maxterms which are stated as follows:
(1) Atomic powered or not submarines
(2) Not submarines or not atomic powered
(3) Submarines or not atomic powered
(4) Submarines or atomic powered
The various relationships which may exist are represented by
the Venn diagrams in Fig. 4-1.
CONNECTIVES AND VARIABLES
Before proceeding it will be necessary to identify and define
the symbology used in Boolean algebra. As may be seen, most of
these symbols are common to other branches of mathematics;
however in Boolean algebra they may have a slightly different
meaning or application.
47
■ Not submarines
-Submarines
A Venn Diagram
Submarines-
- Not submarines, not
atomic powered
■ Atomic
Fig. 4-1 . The Venn diagram.
or x
The equal sign, just as in conventional math-
ematics, represents a relationship of equiva-
lence between the expressions so connected.
The dot or small x indicates the logical product,
or conjunction of the terms so connected. The
operation is also frequently indicated with no
symbol use, i.e., A«B = A x B = AB. Most
generally referred to as the AND operation,
the terms so related are said to be "ANDed."
The plus sign indicates the logical sum opera-
tion, a disjunction of the terms so connected.
Usually called the OR operation and the terms
so connected are said to be ORed.
48
The vinculum serves a dual purpose. It is at the
same time a symbol of grouping and of opera-
tion. As a sign of operation it indicates that the
term(s) so overlined are to be complemented.
Complement can be defined as "a Boolean op-
eration whose result is the same as that of
another operation but with the opposite sign;
thus, OR and NOR operations are comple-
mentary." As a symbol of grouping it collects
all terms to be complemented together. Terms
so overlined are often said to be negated, the
process of taking the complement is then called
negation.
( ) These familiar signs of grouping are used in the
customary fashion to indicate that all terms so
contained are to be treated as a unit.
A,B, etc. Various letters are used to represent the vari-
ables under consideration, generally starting
with A. Since the variables are capable of being
in only one of two states the numerals and 1
are the only numbers used in a Boolean expres-
sion.
APPLICATIONS TO SWITCHING CIRCUITS
Since Boolean algebra is based upon elements having two
possible stable states, it becomes very useful for analyzing switch-
ing circuits. The reason for this is that a switching circuit can be in
only one of two possible states. That is, it is either open or it is
closed. We may represent these two states as and 1 respectively.
The basic switching operations are discussed below. All other
switching operations (even the most complex) are merely combina-
tions of these basic operations.
Let us consider the Venn diagram in Fig. 4-2A. Its classes are
labeled using the basic expressions of Boolean algebra. Note that
there are two elements, or variables, A and B. The shaded area
represents the class of elements that are A«B in Boolean notation
and is expressed as:
f(A,B) = A«B
49
A
B
f(A,B) = AB
1
1
1
1
1
4% Venn Diagram
+l HA
"1" ,\>"0"
£
"V "0"
. ( Load VJ
■J AND switching circuit
e
A
B
©
Truth table
AB
Logic diagram
mechanization of f(A,B) = AB
Fig. 4-2. The AND operation.
The other three classes are also indicated in Fig. 4-2A. This ex-
pression is called an AND operation because it represents one of the
four minterms previously discussed. Recall that AND indicates
class intersection and both A and B must be considered simultane-
ously.
We can conclude then that a minterm of n variables is a logical
product of these n variables with each variable present in either its
noncomplemented or its complemented form. It is considered an
AND operation.
For any Boolean function there is a corresponding truth table
which shows, in tabular form, the true conditions of the function for
each state its variables can be in. In Boolean algebra, and 1 are the
symbols assigned to the variables of any function. Figure 4-2B
shows the AND operation function of two variables and its corre-
sponding truth table.
You can see that this function is true if you think of the logic
involved; AB is equal to A and B which is the function f(A,B). Thus,
if either A or B takes the condition of 0, or both take this condition,
the function f(A,B) = AB is equal to 0. But if both A and B take the
condition of 1, the AND operation function has the condition of 1.
Figure 4-2C shows a switching circuit for the function f( A ,B) =
AB. There will be an output only if both A and B are closed. An
output in this case equals 1. If either switch is open (0 condition),
there will be no output or 0.
50
In any digital equipment, there will be many circuits like the
one shown in Fig. 4-2C. In order to analyze circuit operation, it is
necessary to refer frequently to these circuits without looking at
their switch arrangements. This is done by doing a logic diagram
mechanization as shown in Fig. 4-2D. This figure indicates that
there are two inputs, A and B, into an AND operation circuit
producing the function (in Boolean algebra form) of AB. This dia-
gram simplifies the circuit diagram by indicating operations without
drawing all the circuit details.
It should be understood that while the previous discussion
concerning the AND operation dealt with only two variables the
same ideas can be applied to any number of variables. For example,
in Fig. 4-3 three variables are shown along with their Venn diagram,
truth table, switching circuit, and logic diagram mechanization.
Consider the Venn diagram in Fig. 4-4A; note that there are
two elements, or variables, A and B. The shaded area represents
the class of elements that are A+B in Boolean notation and is
expressed in Boolean algebra as:
f(A,B) = A + B
A-B-C r*_2 A-B-C
A-B-C
AaND switching circuit
A
B
c
f(A.B,C)
= ABC
1
1
1
1
1
1
1
1
1
1
1
1
1
©
Truth table
ABC
§5% Logic diagram
mechanization of f(A,B,C) = ABC
Fig. 4-3. The AND operation (three variables).
51
A
B
f(A,B)
= A + B
1
1
1
1
1
1
1
^j%Venn diagram f-^
£
Truth table
A + B
jrQr
%£J Logic diagram
mechanization of f(A,B) = A + B
e
Or switching circuit
Fig. 4-4. The OR operation.
This expression is called an OR operation for it represents one of
the four maxterms previously discussed. Recall that OR indicates
class union, and either A or B or both must be considered. A
maxterm of n variables is a logical sum of these n variables where
each variable is present in either its noncomplemented or its com-
plemented form.
In Fig. 4-4B the truth table of an OR operation is shown. You
can understand this truth table if you think of A+B as being equal to
A or B. Thus if either A or B takes the value 1, f(A,B) must equal 1.
If neither A nor B takes the value 1, the function equals zero.
Figure 4-4C shows a switching circuit for the OR operation. It
contains two or more switches in parallel. It is apparent that the
circuit will transmit if either A or B is in a closed position (that is,
equal to 1). If, and only if, both A and B are open (equal to 0) the
circuit will not transmit.
The logic diagram for the OR operation is given in Fig. 4-4D.
This means that there are two inputs, A and B, into an OR operation
circuit producing the function in Boolean form of A+B. Note how
this diagram is different from that in Fig. 4-2D.
As in the discussion of the AND operation, the OR operation
may also be used with more than two inputs. Figure 4-5 shows the
OR operation with three inputs.
52
The shaded area in Fig. 4-6A represents the complement of A
which in Boolean algebra is A and read as "NOT A" . The expression
f(A) equals A is called a NOT operation. The truth table for the NOT
operation (Fig. 4-6B) is explained by the NOT switching circuit. A
NOT circuit must take a signal that is injected at the input and
produce the complement of this signal at the output. Thus, in Fig.
4-6C it can be seen that when switch A is closed (equal to 1), the
relay opens the circuit to the load. When switch A is open (equal to
0) the relay completes a closed circuit to the load. The logic diagram
for the NOT operation is given in Fig. 4-6D. It shows that A is the
input to a NOT operation circuit and gives an output of A. The NOT
operation may be applied to any operation circuit such as AND or
OR.
The shaded area in Fig. 4-7A represents the quanti ty A O R B
negated. This figure re presents the minterm expression A+B; that
is, A OR B negated is_A OR B and by application of DeMorgan's
Theorem is equal to AB.
The truth table for the NOR operation is shown in Fig. 4-7B.
The table shows that if neither A or B is equal to 1, then f(A,B) is
equal to 0. Furthermore , if A and B are equal , then f(A,B) equals 1 .
^% Venn diagram
Ia Tb 1 c
"1" Vo"" 1 \o"" 1 \'°"
i T , T
A
B
c
f(A,B,C) =
= A+B+C
1
1
1
1
1
1
1
1
1
1
1
1
Truth table
A^y
A+B+C
[fl Logic diagram
mechanization of f(A,B,C) = A+B+C
OR switching circuit
Fig. 4-5. The OR operation (three operations).
53
A
f(A) = A"
1
1
Venn diagram
kf Truth table
Xr,
"0"
£
rh [ Load
%& NOT switching circuit
o
Logic diagram
mechanization of f(A) = A
Fig. 4-6. The NOT operation.
A
B
A + B
f(A,B) '
= A + B
1
1
1
1
1
1
1
1
©
Truth table
' ir • "0" T'«V'i
,_:°\'
m
I NOR switching circuit I Load
%Q Logic diagram
mechanization of f(A,B) = A + B
Fig. 4-7. The NOR operation.
54
The NOR operation is a combination of the OR operation and
the NOT operation. The NOR switching circuit in Fig. 4-7C is the
OR circuit placed in series with the NOT circuit. If either switch A,
switch B, or both are in the closed position (equal to 1), then there is
no transmission to the load. If both switches A and B are open (equal
to 0), then current is transmitted to the load.
The logic diagram mechanization of f(A,B) = A+B (NOR
operation) is shown in Fig. 4-7D. It uses both the OR logic diagrams
and the NOT logic diagrams. The NOR logic diagram mechanization
shows there are two inputs, A and B, into an OR circuit producing
the function in Boolean form of A+B. This function is the input to
the NOT (inverter) which gives the output, in Boolean form, of
A+B. Note that the whole quantity of A+B is complemented and
not the separated variables.
The shaded area in Fig. 4-8A represents the quantity A AND B
negated (NOT), and is a maxter m exp ression. Notice that AB is
equal to the maxterm expression A+B.
A
B
AB
f(A.B) = AB
1
1
1
1
1
1
1
1
o
Truth table
o
AB
<i>
AB
Logic diagram
mechanization of f(A,B)=AB
X
■"' r-h
"0"
D—
e
m
NAND switching circuit
Fig. 4-8. The NAND operation.
55
The truth table is shown for the NAND operation in Fig. 4-8B.
When A and B equal 1 , then f(A,B) is equal to 0. In all other cases,
the function is equal to 1.
The NAND operation is a combination of the AND operation
and the NOT operation. The NAND switching circuit is shown in
Fig. 4-8C. Note that the AND circuit is in series with the NOT
circuit. If either switch A or B is open (equal to 0), then current is
transmitted to the load . If both switches A and B are closed (equal to
1), then there is no transmission to the load.
The logic diagram mechanization of f(A,B) = AB (NAND oper-
ation) is shown in Fig. 4-8D. The AND part of the diagram and the
NOT part of the diagram show that there are two inputs, A and B,
put into the AND circuit. The result is then input to the NOT circuit
which gives the output, in Boolean form, of AB. Note that the entire
quantity AB is complemented and not the separate variables.
NOTE: The logic diagrams in Figs. 4-7 and 4-8 do not conform
to the American Standard Logic Symbology (MIL-STD) . They were
drawn in this fashion to illustrate a point in the text, normally they
will be drawn as shown in Fig. 4-9.
The exclusive OR operation is actually a special application of
the OR operation. In this operation either A or B must be true in
order for the function to be true; however, if both are true at the
same time the function will be false.
As shown by the Venn diagram (Fig. 4-10A), this operation
must be assigned a special class since it does not conform to any of
the minterm or maxterm classes previously discussed.
In the mechanization of this operation (Fig. 4-10C) the
switches are mechanically linked together so that one or the other,
but not both, may be closed at a time. The truth table for this
operation is shown in Fig. 4-10B and the logic symbol in Fig. 4-10D.
FUNDAMENTAL LAWS AND AXIOMS OF BOOLEAN ALGEBRA
The laws and axioms of Boolean algebra are used to simplify
any Boolean expression. They are listed below. Figures 4-11
A
o AB
A
A+B
)
NOR
B
KJ
NAND
Fig. 4-9. American Standard logic symbology for the NOR and the NAND
operations.
56
K9 Venn diagram
X. I—
f(A,B) = AB+BA
©
Truth table
Jlj
AB + BA
Load
Logic diagram
exclusive "OR"
function
^fi^Exclusive OR switching
circuit
Fig. 4-10. The EXCLUSIVE OR operation.
through 4-20 show the truth tables, logic diagrams, and mechaniza-
tion for these laws and axioms.
I . Law of Identity
A = A
II. Law_of Complementarity
l.M_f=0
2. A+A = 1
III. Idempotent Law
1. AA = A
2. A + A = A
A = A
A
"1"
A
A
1
1
Fig. 4-1 1 . Law of identity.
57
IV. Commutative Law
1. AB = BA
2. A + B = B + A
V. Associative Law
1. (AB)C = A(BC)
2. (A + B) + C = A + (B + C)
VI. Distributive Law
1. A(B+C) = (AB) + (AC)
2. A + (BC) = (A + B) (A + C)
VII. La w of Du alization (DeMorgan's Theorem)
1. (A + B)_= AB
2. (AB) = A + B
VIII. Law of Double Negation
A" = A
IX. Law of Absorption
1. A(A + B) = A
2. A + (AB) = A
Axioms
1. A + = A
2. A • =
3. A + 1 = 1
4. A • 1 = A
(The variable A may be 1 or 0.)
Equal
10
A**0
©
to
A S"*
HOR_ckI I IX.
jl
A
A
A-t-A
1
1
1
'
Fig. 4-12. Complementary law.
58
o
AA =
e
A-
A A A + A
M
EQuaJ
AA = A
Equal
A+ A = A
A + A =A
Fig. 4-13. Idempotent law.
BOOLEAN EQUATION SIMPLIFICATION AND MECHANIZATION
As you have seen , Boolean algebra comprises a set of axioms
and theorems which are useful in describing logic equations such as
those used in computer technology. Likewise, these laws and
axioms are used to simplify logic equations so that logic conditions
can be designed in their simplest and most economic form. For
example, the equation below is a logic equation which describes the
logic circuit (Fig. 4-21A) in Boolean terms.
f = AC + AD + BC + BD
Boolean algebra can be used to simplify the logic equation.
f = AC + AD + BC + BD
= A(C + D) + B(C + D)
= (A + B) (C + D)
The logic circuit arrangement for the simplified expression is
shown in Fig. 4-21 B. Factors such as the loading and standardi-
zation of logic circuits may dictate the use of other than the
simplest possible Boolean expression. In this discussion, the
only concern is the simplification of equations. Other design
considerations are not dealt with.
Consider the following as a second example:
EXAMPLE: Simplify the logic equation,
f = ABC + ABD + AC + ABCD + AC
59
AB = BA
"1" "1"
• AB
AND ckt
y-
•1" "V
BA
AND ckt
H
A
B
AB
1
1
1
1
1
B
A
BA
1
1
1
1
1
+ A
A + B
ORckl
B+A
OR ckt
A
B
A+B
1
1
1
1
1
1
1
B
A
B+A
1
1
1
1
1
1
1
> Equal
A+ B = B + A
Fig. 4-14. Commutative law.
60
SOLUTION: Rearrange terms and factor as follows:
f = ABC + AC + ABCD + AC + ABD
= A(BC + C) + A(BCD) + ABD
Apply the complementary law to (BC + C) and (BCD + C). Then:
f = A(B + C) + A(BD + C) + ABD
Apply distributive law. Then:
f = AB + AC + ABD + AC + ABD
f = (AB + ABD) + AC + AC + ABD
Apply the law of absorption to (AB + ABD) and rearrange terms.
Then:
f = AB + AC + AC + ABD
This equation is the easiest to mechanize. However, the simplifica-
tion process could be carried one step further by factoring, in which
case:
f = A(B + C) + A(C + BD)
The foregoing examples of simplification show the process to
be rather difficult at first. For the beginner there is no positive
indication that the simplest possible logic equation has been
reached. You must learn by experience. Repeated use of these
theorems is the only solution. Simplification theorems are of
greatest value in the preliminary stages of simplification, or in the
simplification of elementary functions.
A second way approach to equation simplification is to use the
Veitch diagram . This type of diagram provides a very quick and easy
way for finding the simplest logic equation needed to express a
given function. Veitch diagrams for two, three, or four variables are
readily constructed (Fig. 4-22). Any number of variables may be
plotted on a Veitch diagram, although the diagrams are difficult to
construct and use when more than four variables are involved.
Because each variable has two possible states (true or false),
the number of squares needed is the number of possible states (two)
raised to a power dictated by the number of variables . Thus , for four
variables the Veitch diagram must contain 2 4 or 16 squares. Five
variables require 2 5 or 32 squares. An eight-variable Veitch diagram
needs 2 8 or 256 squares— a rather unwieldy diagram. If it becomes
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A = A
O^O
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A I A I A
0__1
1 1
"1"
L-—-J L_j — I
l> Equal <l
A = A
••0"
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"1"
Load
Fig. 4-18. Law of double negation.
necessary to simplify logic equations containing more than six
variables, other methods of simplification should be used.
An exploded view of a four variable Veitch diagram is shown in
Fig. 4-23. Note the division of the diagram into labeled columns and
rows. The entries into the diagram are placed in these columns and
rows in accordance with the function values for a given Boolean
expression.
Looking at the square in the upper left corner of the main
Veitch diagram in Fig. 4-23, and using the extensions, it is seen that
it contains the variables ABCD; the next lower block contains
ABCD; the next lower block contains ABCD] and the block in the
lower left corner contains the variables ABCD . All of the squares in
the diagram are similarly identified. Note that the term AC is
contained in each of the four terms just discussed. Ac-
cording to the distributive law, the variables B and D can be
dropped, because they appear in both asserted and complemented
form. Thus, the left vertical column identifies the terms AC. This is
proven by the equation:
68
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Simplifying
f(A,B,C,D, = AC+AD+BC+BD
= A(C+D)+B(C+D)
= (C+D) (A+B)
B
— .
D
^
J BD
C
D
A
B
y
D)
p-X,c,
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i y
B)
"N
J f=AC+AD+BC+BD=
y (A+R)fn+D)
)_^
^w
Fig. 4-21 . Simplified logic circuitry resulting from simplifying logic equations.
AC = ACQ)
= AC_(B + B)_
= ABC + ABC
= ABC (1) + ABC (1)
= ABC (D + D)_+ ABC (D + D)
= ABCD + ABCD + ABCD + ABCD
The final expression represents four of the maxterms of the
term AC. Also note that a two-variable term is represented by four
squares. A study of the diagram will reveal that a term with one
variable is represented by eight squares, a three-variable term by 2
squares , and a four-variable term by 1 square .
To illustrate the use of the Veitch diagram, the logic equation
f = ABC + ABD + AC + ABCD + AC
71
A A
B
B
2 Variables
A
A
B
p"
C
c
C
3 Variables
A
A
D
B
D
B~
n
C
c
C
4 Variables
E
A
A
A
A
B
D
D
B
D
C
c
C
C
C
5 Variables
[
A
A
E
A A
B
D
D F
B
D —
B
D F
B
d"
C
(
C
C
c
6 Variables
Fig. 4-22. Veitch diagrams.
will be used. Because there are four variables, a four variable
Veitch diagram is needed. The step-by-step process is as follows:
Step 1. Draw the appropriate Veitch diagram. See Fig. 4-24.
Step 2. Plot the logic function on the Veitch diagram, term by
term. This is accomplished by placing a "1" in each square rep-
resentative of the term. (Use Fig. 4-24 to identify the squares and
Fig. 4-25 to understand the plotting of the terms on the diagram.)
The term ABC in the equation (f = ABC + ABD + AC + ABCD +
AC) is identified in the Veitch diagram by squares 2 and 6. The
derivation is as follows: ABCD + ABCD = ABC (D + D) = ABC (1)
+ ABC
The_term ABD^identified by squares 1 and 2 as follows: ABCD
+ ABCD + ABD (C + C) = ABD (1) = ABD _
For the tejrm_AC, usejsquares 1, 5, 9, and 13: ABCD -FABCD
+_ABCD + ABCD = ABC (D_+ D) + ABC (D + D) = ABC (1) +
ABC (1) + AC ( B + B) = AC (1) = AC
The term ABCD, identified by square 16, is self-ex-
planatory. The term AC, shown in squares 3,7,11, and 15, canbe
figured as follows: A"BCD + ABCD + ABCD + ABCD = ABC (D +
72
5
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73
A
A
D
ABCD
1
ABCD
2
ABCD
3
ABCD
4
B
_
—
— —
ABCD
ABCD
ABCD
ABCD
5
6
7
8
D
_
— _
ABCD
ABCD
ABCD
ABCD
B
9
10
11
12
— — —
_ _
_ _ _
_
ABCD
ABCD
ABCD
ABCD
D
13
14
15
16
C
C
C
Note: The numbers in each
square are for the purpose
of illustration only.
Fig. 4-24. Identifying the squares of a Veitch diagram.
D) + ABC (D + D) = ABC (1) + ABC (1) = AC (B + B) = AC (1) =
AC
Step 3. Obtain the simplified logic equation by using Fig. 4-26
and observing the following rules:
B
A
A
D
ABCD
1
ABCD
1
ABCD
1
ABCD
ABCD
1
ABCD
1
ABCD
1
ABCD
D
B
ABCD
1
ABCD
ABCD
1
ABCD
ABCD
1
ABCD
ABCD
1
ABCD
1
D
C
C
C
Fig. 4-25. Plotting of the logic function.
74
a. If l's are located in adjacent squares or at opposite ends of
any row or column, one of the variables may be dropped.
b. If l's fill any of the following locations, two of the variables
may be dropped: any row or column of squares, any block of four
squares, the four end squares of any adjacent rows or columns, or
the four corner squares .
c. If l's fill any of the following locations, three of the variables
may be dropped: any two adjacent rows or columns, the top and
bottom rows, or the right and left columns.
d. To reduce the original equation to its simplest form, you
must simplify until all l's have been included in the final equation.
The digit "1" may be used more than once, and the largest possible
combination of l's, in groups of 8, 4, 2, or as a single 1 (block),
should be used.
Squares_l,5,9, and 13 are combined (Fig. 4-26) using rule (b) to
yield AC (l's in B and B cancel).
Squares 3,7,11, and 15 are combined using rule (b) to yield AC.
Squares 1,2,5, and 6 are combined using rule (b) to yield_AB.
Squares 15 and 16 are combined using rule (a) to yield ABD.
To keep track of the squares combined, draw loops around the
combined squares. When you do this, the Veitch diagram takes on
the appearance shown in Fig. 4-26.
All l's have been used; therefore, a logic equation can now be
written
A
A
B
3,
4
D
Pi
2,
5,
6,
7,
8
D
B -:
9,
10
11,
12
13,
] 14
D
Q
lis.)
C
C
C
Fig. 4-26. Derivation of resultant.
75
A
A
B
1
2,
3
4
B
5
6
7
8
C
C
c
Fig. 4-27. Three-variable Veitch diagram showing statement True,
f = AB + AC +AC + ABD
which agrees with the simplified logic equation obtained by the use
of the simplifying theorems.
A Veitch diagram provides a convenient means of finding the
complement of a logic equation . This is done by plotting the original
equation on a Veitch diagram and then putting l's on another Veitch
diagram everywhere except where the original diagram has l's. An
example will illustrate the procedure.
EXAMPLE:
If: f = ABC
What is f?
A three variable Veitch should give the answer. The original
equation is first plotted as shown in Fig. 4-27.
On another Veitch diagram, all squares which do not have a 1 in
the original diagram are assigned a 1 (Fig. 4-28).
Now the equation for f can be written. Squares 3, 4, 7,_and 8
combine to form A; squares 5,6,7, and 8 combine to form B; and
squares 1,5,4, and 8 combine to form C. Therefore, the equation for
f is:
f = A+¥+C
which agrees with the result obtained by directly applying DeMor-
gan's Theorem.
In the earlier discussion of logic operations, switching circuits
were used to illustrate the various operations. These switching
circuits were actually the mechanization of the logic operations
using conventional single-pole double-throw switches. Before
76
A A
B
£l
2
( 3l
4JS
B
( &-
6,
V 7;
^
w
C
C
c
Fig. 4-28. Three-variable Veitch diagram showing statement complemented.
using the actual logic symbols, the conventional switches are again
used to mechanize an equation. The equation:
f = AB + AC + AC + ABD
will be mechanized.
It will be recalled that the AND function used a series switch-
ing circuit, and the OR function used a parallel switching circuit.
Therefore, the mechanization of the above equation is as illustrated
in Fig. 4-29. This diagram illustrates the AND and OR functions.
The AND functions are each series-connected switch grouping of
the four possible parallel paths— the OR function. The logic dia-
gram for the above equation and mechanization are shown in Fig.
4-30, which uses the logic symbols for the AND and OR gates. A
Switch A
— ofo— —
I
T
-Cio T
I F
Switch C
Switch D
■*£
J>i
F
Vol"
St
f = True when LIT and False when not LIT
Fig. 4-29. Mechanization of a logic equation.
77
logic equation can be always mechanized by a switching network.
This involves the following four steps:
1. Construct a truth table.
2. Write the logic equation.
3. Simplify the equation, if possible.
4. Draw the required switching network.
You are encouraged to apply these four steps to several
hypothetical problems.
Consider the following equations:
1. f = AB+AB + AB
2. f = A + B
Equation 1 is the sum of three Boolean terms , each of which is the
product of two variables (A and B) . Each variable is represented in
either its true or complemented form. Equation 2 represents the
sum of the two variables A and B when B is complemented. Equa-
tion 1 is a minterm expression of the two variables, and equation 2 is
a maxterm expression of these variables.
In general , a minterm expression of n variables is defined as
the product of these n variables where each variable is expressed in
either its true or complemented form. A maxterm of n variables is
the sum of these n variables where each variable is added in either
its true or complemented form. Consequently, there are four min-
Fig. 4-30. Mechanization of a logic equation using logic symbols.
78
Miniterm
Maxterm
1
ABC
16
A+B+C
3
ABC
14
A+B+C
5
ABC
12
A+B+C
7
ABC
10
A+B+C
9
ABC
8
A+B+C
11
ABC
6
A+B+C
13
ABC
4
A+B+C
15
ABC
2
A+B+C
Fig. 4-31. Minterms and maxterms of variables A, B, and C.
terms of two variables, and they are (AB, AB, AB AND AB).
Likewise ,_there_are four maxterms of two variables. They are (A +
B), (A + B), (A + B) and (A + B).
There are eight minterms and eight maxterms of three vari-
ables as shown in Fig. 4-31. As might be expected, there are 2 n
minterms and 2" maxterms when n variables are considered.
Observe that the minterm identified by an odd number in the
upper left corner of each block in the left column relates to the next
higher even number in the right column in accordance with DeMor-
gan's Theorem. For example, the maxterm in block #2 is the
complement of the minterm in block #1.
79
Chapter 5
Introduction to Programming
The process of writing instructions to control the operation of a
computer is called programming. Most of the remaining chapters in
this book will deal with programming in one form or another so we
will only briefly describe the basic technique at this point.
In general , computer programming refers to the analysis and
planning of a problem solution. The phase of instruction writing is
referred to as coding. Here are a few of the concepts involved in
programming.
Binary Operation: The programming process will be de-
scribed in terms of the most common form of digital computer. This
machine operates internally entirely in binary (base 2) arithmetic
logic, and is arranged so that information is stored and accessed in
units termed words. The ATARI uses words that are 8 bits in size.
Decimal Operation: The other broad class of computers
operates logically in the decimal system (although decimal digits
are fabricated within the machine by combinations of bits) and
stores and accesses its information in units of individual characters
such as digits or letters. This machine is referred to as a character-
addressable or variable-word-length computer.
Notation: The ATARI operates internally using the binary
number system. Skilled programmers often work using the octal
(base 8), or hexadecimal (base 16) systems. These systems are
simply conveniences for programmers to use while they work.
However, the discussion here will be in terms of decimal values to
80
simplify understanding of computer principles. It must be kept in
mind that the basic nature of the machine is binary.
Number Operations: The purpose of a computer is to ma-
nipulate information that is stored within the machine in the form of
binary numbers. These numbers can be treated as symbols and can
represent alphabetical information. They can also be treated as
numbers and can be used arithmetically. Each word contains one
number and its associated algebraic sign (positive or negative) . The
instructions which dictate the operations to be performed on such
numbers (data) are also numbers and are also as a single word in the
same physical medium as the data. The stored programming con-
cept presumes that there is no physical difference between these
two types of numbers and that the instruction numbers may also be
manipulated, in the proper context, as data.
Addresses: Each word in storage is assigned an address in
order to refer to it, in a manner analogous to postal addresses. The
addressing scheme is part of the hardware of the machine, and is
wired in permanently. Word addresses range from zero to the
storage size of the machine. Any word may be loaded with any
desired information. Some of this information is the data of the
problem being processed; the rest is the instructions to be exe-
cuted. The machine is designed basically to execute instructions in
the order in which they are stored, advancing sequentially through
the instruction words at addresses that increase by one.
Instruction Format: Each instruction contains two basic
parts: (1) a coded number that dictates what operation is to be
performed and (2), the address of the word (data) on which to
perform that operation.
Programming for a digital computer could be done in binary,
but becomes increasingly difficult as programs get longer. For this
reason, programmers prefer to work in languages that are at a
higher level. In higher-level languages, mnemonic operation codes
are used in place of numbers, and all absolute machine addresses
are replaced by symbols. These alterations greatly speed up the
work of the programmer. High-level languages permit a format that
fits the problem rather than the machine . BASIC is one such lan-
guage that is readily adapted to both home and business applica-
tions.
BASIC
BASIC means .Beginner's Ail-Purpose Symbolic instruction
Code .It is a high-level language that a beginning programmer can
81
understand with relative ease . An interpreter that changes the in-
structions in BASIC to terms that can be used by the machine must
be present in the computer when a BASIC program is used. BASIC
was developed at Dartmouth College in the sixties for educational
purposes. It is, in fact, probably the simplest higher-level language
available at this time.
BASIC is widely implemented on microcomputers like the
ATARI 800, and it is also available on most large scale computers.
THE PROGRAMMING PROCESS
Programming is a creative process because it is primarily a
problem-solving job. You, the programmer must select the best or
most effective and efficient solution for a given problem. Once a
solution is developed, you must then code it into a language the
computer understands, so that the computer can help solve the
problem.
Before beginning to write a program to solve a given problem,
there are some basic considerations with which you should become
familiar. In general, there are four objectives in programming:
1 . Economy of storage
2. Speed of computation
3. Accuracy
4. Simplicity
With these four basic objectives in mind , let's see what steps
are involved when programming a computer.
1. Accurately define the problem— exactly.
2. Propose a feasible and economical solution.
3. Redefine the problem in terms of what the computer is
expected to do.
4. Prepare a flowchart of the computer solution.
5. Code the solution.
6. Debug (remove errors from) the program.
7. Document the program.
Before you can solve a problem, you must understand the
problem. First make a list of all available data. Then define the
problem in terms that are understandable terms both to yourself and
others who might be involved with the problem. Finally, propose a
method of solving the problem. If there is more than one possible
solution— and there usually is— choose the one that best fulfills the
82
four basic objectives of programming, especially simplicity.
When you define a problem and then propose a feasible solution
to it, you are developing what is called an algorithm, or a step-by-
step solution to a specific problem. Once this is accomplished, you
must tailor the solution to fit the computer's capabilities, or the
solution will be useless. You must define both the problem and
solution in terms of what the computer can do.
Next, you should draw a flowchart of the solution. Basically, a
flowchart is the algorithm illustrated in graphical form. See Chapter
13 for more details. After the solution is flowcharted, it can be
coded into a language that the computer understands. You must then
check the program for errors and finally, document it.
LET'S WRITE A PROGRAM
We could continue on the theory of program writing for several
more pages, but to get you acquainted with the practice, let's jump
right in and try writing a simple program . If this is your first attempt
at such an undertaking, there will still be a few hazy areas once we
are finished, but you should have a good basic knowledge which will
enable you to attempt the more advanced problems later on in the
book.
Remember, to write a computer program, you must have the
following:
1. A precise definition of what the program is to accomplish.
2. A detailed, step-by-step plan of how the program goals will
be achieved.
3. Knowledge of the programming statements can be used to
implement the step-by-step plan.
Define precisely what the program is to accomplish:
You are more than likely familiar with the Fahrenheit temperature
system. You have also probably heard of the Celsius temperature
system that is supposed to eventually replace the Fahrenheit sys-
tem. So let's write a temperature conversion program. Here's
exactly what the program is to accomplish:
This program is to provide a fast and easy means of converting
between the Celsius and Fahrenheit temperature systems.
The direction of the conversion is to be specified; then the
temperature that is to be converted must be entered. The
converted temperature is then displayed or printed.
83
This precise definition of what the program is to accomplish is
the first and most important part of program writing. With this out of
the way, we can continue to the second step.
Make a step-by-step plan of how the program goals will
be achieved: There will usually be more than one solution to a
problem, so the exact method of developing the step-by-step plan
will differ with each programmer. In most cases, however, it is best
to rely on the technique known as flowcharting. A flowchart is
simply a set of symbols that indicate the steps of program execu-
tion. Each block in a flowchart usually contains one and only one
instruction. The standard flowcharting symbols appear in Fig. 5-1.
The terminal symbol is used to indicate the beginning and
ending points of a program; words like "start," "end," or "stop" are
normally written inside it. The input/output symbol is used to
indicate an input or output operation. The decision symbol indicates
a decision or yes/no question, with the nature of the decision
normally written inside the symbol. As might be imagined, the yes
and no paths provide two directions for the program to continue in,
depending upon the result of the decision.
CD
(A) Terminal start
or stop
(B) Input/output
(C) Decision
o
(D) Process
(E) Connector
(F) Keyboard
(G) Document
(H) Arrows, flow
lines
Fig. 5-1. Flowcharting symbols.
84
The process symbol is a rectangle. It indicates operations such
as add, subtract, load accumulator, or store. The circle is used to
refer from one point to another when it is difficult or impossible to
physically connect them with a line. For example, corresponding
letters placed in these circles could show the continuation of a
program from one sheet of paper to another.
The keyboard symbol is used to represent an output to a video
terminal or input from a keyboard. The document symbol generally
represents an output on a printer. Finally, the arrowheads and the
flow lines depict the relationship between symbols and identify
operational sequences.
To write a flowchart for our sample program , we must take the
description of exactly what the program is to accomplish and pro-
vide the appropriate flowchart symbol for each step.
First, each program must have a begin-
ning point.
Next a prompt must indicate what infor-
mation the user should input.
Now, the description says we will have to
input a temperature in either Celsius or
Fahrenheit. We can change this each
time the program is run, so the informa-
tion should come from the keyboard.
Now the computer must perform an op-
eration (convert the temperature in one
system to the other).
Now the results of the conversion (the
output) should be printed.
( Begin J
Print
prompt
Convert
temperature
Print both
temperatures
All programs must have an Ending Point .
( Stop )
85
Implement the step-by-step plan with programming
statements: Before we can actually write the program, we must
have an understanding of standard programming statements. The
BASIC programming statements used in this program are shown in
Table 5-1. Let's apply these statements to accomplish the steps
shown in the program flowchart.
The first step in the flowchart is "Begin" . Since we do not need
a program line to "begin", we will take this opportunity to write a
REMark statement that gives the title of the program:
10 REM **CELSIUS TO FAHRENHEIT**
20 PRINT "CELSIUS TEMP"
The second statement PRINT "CELSIUS TEMP", causes the
computer to display the question, CELSIUS TEMP? The second
step in the flowchart calls for an input ; in this case , the temperature
in the Celsius. So the response to the next line of the program (30)
will come from the keyboard. We need to select a name for the
variable which will receive the data. How about "C" for Celsius?
30 INPUT C
The next step in the flowchart calls for a computer operation:
the Celsius temperature must be converted to Fahrenheit. To
convert the Celsius temperature to Fahrenheit, the Celsius temp-
erature is multiplied by 1.8 and then 32 degrees is added to the
results. So our next statement will be:
40 LETF = 1.8*C+32
The next step in the flowchart calls for printing the results of
the computation.
50 PRINT C; "C EQUALS ";F;"F"
The last step on the flowchart is the end of the program so we'll
write
60 END
Here is the initial version of our program
86
Table 5-1. BASIC Programming Statements.
Atari Programming Statements
Let
Assigns names and values to
variables.
PRINT "string literal"
Prints on paper or displays
on screen the exact charac-
ters enclosed by quotation
marks.
PRINT variable name
Prints or displays numerical
content of variable.
PRINT expression
Computes mathematical expres-
sion; then prints or displays
the result.
PRINT item; item
List of items printed or dis-
played on same line without
added spaces.
PRINT item , item
List of items printed or dis-
played on same line aligned
into columns
REM
Remarks can be included in
program to document or ex-
plain. Ignored by computer.
Goto
Alters order of program
execution.
If... then
Makes decisions based on re-
lational tests.
Read.. .data
Supplies data items from pro-
gram-resident list.
Input
Supplies data items from
keyboard.
Stop
Stops program execution.
Deluxe Programming Statement
On. ..goto
Program branches made to
computed line number.
87
10 REM **CELSIUS TO FAHRENHEIT**
20 PRINT "CELSIUS TEMP"
30 INPUT C
40 LETF = 1.8*C + 32
50 PRINT C; "C EQUALS ";F; "F"
60 END
And here's how the program will look when executed:
CELSIUS TEMP?
15
15 C EQUALS 59F
To satisfy our initial program requirements, we must write
another program to provide a means to convert Fahrenheit to
Celsius. In general, we merely reverse the operations of the first
part of the program to come up with the following scheme.
10 REM "FAHRENHEIT TO CELSIUS**
20 PRINT "FAHRENHEIT TEMP";
30 INPUT F
40 LET C = 5/9* (F- 32)
50 PRINT F; "F EQUALS " ;C;"C"
60 END
Assuming we have a Fahrenheit temperature of 59 degrees,
what is its Celsius equivalent?
Here's how the program will look when executed.
FAHRENHEIT TEMP? (The computer asks)
59 (You type this in)
The computer will print or display the following:
59 F EQUALS 15 C
LINE NUMBERS
From the previous discussion, we know that a BASIC program
is composed of a series of statements which manipulate data. Each
BASIC statement occupies one line. Each line is identified by a
number which appears at the beginning of the line. Obviously, no
two lines may use the same number. In most cases, the computer
88
executes the statements in the order of their line number, and
these line numbers are normally increments of ten; that is, 10, 20,
30, etc. This gives the programmer nine numbers between state-
ments to add other statements later to expand the program if
necessary .
BASIC STATEMENTS
Earlier in this chapter you were introduced to BASIC state-
ments , but since these must be thoroughly understood to program
in BASIC, let's review these statements and go into more detail.
There aren't really very many to learn, so make sure you know and
understand each before continuing with programming.
Let: The let or replacement statement is used to assign a value
to a variable name. For example, in our temperature conversion
program, 40 LET C = 5/9*(F-32) assigns C the value of 5/9 times
the Fahrenheit temperature minus 32 degrees.
Successive let statements can be used to place a number of
constants into different variables. For example, suppose we wish to
place the four constants 22, 32, 43, -12 in variables A, B, C, and D
respectively. Four let statements could be written as follows:
10 LET A = 21
20 LET B = 32
30 LET C = 43
40 LET D = - 12
The four constants 21 , 32, 43, and - 12 are then assigned to the four
variables A, B, C, and D.
Read and Data Statements: While the let statement allows
for the placement of a constant into a variable, its use becomes
unwieldy if a large number of constants are to be entered. In the
above example , four statements were required to enter four con-
stants. The read and data statements are used to overcome this
difficulty. To assign the four constants in the above example, only
two statements are required. One statement identifies the con-
stants (data). It would be written:
10 DATA 21, 32, 43, -12
The read statement assigns these constants to the variables. It
would be written:
20 READ A,B,C,D
The first constant is assigned to the first variable listed, the second
constant to the second variable, and so forth. Thus, with only two
statements we could assign dozens of constants to corresponding
variables. The read and data statements are the most common way
of entering constants into the computer.
Print Statement: Once the program has finished, we need a
means of displaying the results . The print statement is used for this
purpose. It consists of the word print followed by a list of the data
and variables to be put on the screen. For example, if we wished to
print out the values of variables A,B,C, and D, we would write:
20 PRINT A, B, CD
When this statement is executed, the constants stored in these
locations are printed.
The print statement also allows a message to be printed. The
message is enclosed in quotation marks. For example, the state-
ment:
30 PRINT "END OF DATA"
causes the words END OF DATA to be printed. Notice the differ-
ence between the two statements PRINT X and PRINT "X". In the
first statement, the value assigned to the variable X is printed. In
the second statement, the message X is printed. To illustrate how
this can be used, consider the program:
50 LET X = 3
60 PRINT "X=",X
Statement number 50 assigns X the value of 3. Statement 60 causes
the message "X=" to be printed. It is followed by the value of X.
This gives a printout of
X = 3
If... then statement: One of the most powerful control
statements in BASIC is the if... then statement. It is a decision-
making statement that allows the computer to choose alternative
courses of action, depending upon the relative size of two constants.
90
Table 5-2. Symbols Used
n the BASIC Programming Language.
Symbol
Meaning
=
is equal to
<
is less than
>
is greater than
< =
is less than or equal to
> =
is greater than or equal to
< >
is not equal to
The two constants can be compared in any of six different ways . The
symbol explaining the relationship of the two constants are shown in
Table 5-2.
The if... then statement takes the form:
10 IF X > THEN 30
This says that if X is greater than , execute statement 30 . If X is not
greater than 0, then the next statement in the sequence is executed.
As you can see, this type of statement is a conditional branch which
depends on the value of X.
Goto Statement: The goto statement is the unconditional
branch statement. It consists of the word goto followed by a line
number. For example, GOTO 160 causes line 160 to be executed
next rather than the line that is next in sequence.
On. ..goto Statement: This statement is a conditional
multiple-branch statement. It is also known as a computed goto
statement. The format is:
10 ON X GOTO 20,30,40
The integer portion of X is evaluated. If X = 1, the program
branches to statement 20. If X = 2, the program branches to
statement 30. If X = 3, the program branches to statement 40.
Although only three possible branches are shown here, the state-
ment can contain as many possibilities as needed. Also, the X may
be a formula or expression rather than a single variable. An expres-
sion such as X = A - B would be evaluated first; then the outcome
would be used to determine the branch. Noninteger values of X will
be truncated to their integer values before being used to determine
the branch . As you can see , this type of statement can become very
complex. However, when properly used, it can do the same job as
many if... then statements.
91
For... To and Next Statement: These statements are used
to control the repeated execution of a program loop. When using
these statements, the program loop begins with the for... to state-
ment and ends with a next statement. The format of the for... to
statement is
15 FOR X = 1 to 100
When this statement is encountered , a counter, X, is set to the first
value on the right side of the equal sign . In the example above , X is
initially set to 1 . The program then executes the statements in the
loop. If the variable X is encountered in any of the statements in the
loop, it is assumed to have the value of 1.
The last statement in the loop is the next statement. Its format
is:
NEXTX
This informs the computer that the first pass through the loop is
complete and that X should be set to its next sequential value. In
this case, X is incremented by 1 to the value 2 and the loop is
repeated. The loop is repeated again and again with X being set to
every value from 1 to 100. Each time the next X statement is
executed, the new value of X is compared with the final value of 100.
This continues until X has assumed all values called for in the
for. . .to statement . The loop is repeated for the last time when X is
set to 100. At this time, the program leaves the loop and executes
the first statement following the next.
As a simple example, consider the loop below
10 FOR X = 1 TO 5
20 PRINT X
30 NEXT X
The computer will set X = 1, then print it. X will then be in-
cremented and the loop repeated . The program above will produce
the following output:
1
2
3
4
5
92
In our example, X was set to all values for 1 to 5. The for. ..to
statement could just as easily have called for all values from 1 to
1000 or from 13 to 20 , etc . The variable which assumes these values
need not be X. Any variable could have been assigned. Most of the
time when a for... to statement is written, a step size of 1 is used. In
our example, X was stepped (incremented) by 1 each time through
the loop. However, other size steps can be specified by the for. ..to
statement. For example the statement:
FOR N = 2 TO 1000 STEP 2
specifies that the variable N will be assigned the values
2,4,6,8,... 1000. The for... to statement can also be told to count
backwards by using the following format:
FOR X = 1000 TO 1 STEP-1
In other words, X is decremented.
Subscripted Variables: It is often convenient to use sub-
scripted variables when programming with BASIC. For example, if
we have a list of 20 numbers to be added, we can call the entire list
by a single variable name. If we call the list A, the first number on
the list could be A ; the second, A 2 ; the third, A 3 ; and so forth. When
entering data from a video terminal or I/O typewriter, the subscript
must be typed on the same line as the variable. For this reason,
subscripts are written in parentheses. For example, A. [ is written
A(l), A is written A(2), etc. Be careful not to confuse subscripted
variables such as X(l) with simple variables composed of a letter
and a numeral such as XI.
In the terminology of BASIC, the list of 20 numbers described
above is called an array. We arbitrarily called the array by the
variable name A. In BASIC, an array name must consist of a single
letter. Since there are only 26 letters, we can use no more than 26
arrays in a single program. The list of 20 numbers described above
is called a one-dimensional array. The 20 numbers in the array are
known by the subscripted variables A(l) through A(20). An array
can sometimes have two dimensions. For example, consider the
numbers shown in Table 5-3. This table contains 20 numbers just
like the list discussed earlier. However, the table is divided into 4
columns of 5 numbers each. Thus, we call this a two-dimensional
array or matrix. The numbers in this type of array are described by
double subcripted variables . If the array is A , the number in the first
93
Table 5-3. A Two-Dimensional Array.
Second Subscript (columns)
w
(1)
(2)
(3)
(4)
31.7
79.6
16.8
11.5
19.9
37.3
87.2
53.6
10.3
94.0
83.2
44.4
76.1
19.9
49.4
29.1
01.7
21.7
57.9
37.3
row and first column is A(l , 1) . By the same token , the third number
in the second column is A(3,2). Arrays are useful when large
amounts of data must be handled nonsequentially or when alterna-
tions of data must be achieved.
Dim Statement: The dim or dimension statement is used to
deal with lists and two-dimensional arrays in BASIC. It allocates
storage and assigns names to the lists and tables to be used. The
dim statement has two formats:
30 DIM A(6)
40 DIM F(10,4)
The first statement defines a list called A and allocates 6 memory
locations for storage. The second statement defines a table (a
two-dimensional array) called F with 10 rows and 4 columns. Sev-
eral lists or arrays may be defined with one dim statement by simply
including the definitions on the same line separated by a comma.
Gosub and Return Statements: In BASIC, as in most lan-
guages, subroutines can be used. An often needed computation can
be written in BASIC, then used by the main program as often as
needed. The gosub statement causes the main program to branch to
the subroutine. A line number following the word gosub tells where
the subroutine is located. For example, the statement gosub 205
tells the program to branch to line 205 and execute the statements it
finds there. The end of the subroutine is signified by a return
statement, which sends execution of the program to return to the
main program. The return causes the statement following the one
containing the gosub to be executed next.
List Command: List is generally used as a command, not as
a statement within a program. It causes the program in the com-
94
puter to be displayed in its entirety. This allows you to review, edit,
or modify the program conveniently without retyping it.
REM Statement: The remark statement lets the program-
mer insert notes, comments, or messages of any kind into the
program. The remarks do not affect the program itself. They simply
allow you to tell what the program is, how it is used, and how to use
it. For example, 10 REM PROGRAM FOR COMPUTING GRADE
AVERAGE will cause the statement PROGRAM FOR COMPUT-
ING GRADE AVERAGE to be printed when the program is listed.
Input Statement: We have seen that data can be assigned to
variables by using the let statement or by using the read and data
statements in pairs. There is also a third method of assigning
values . It involves the use of the input statement . The format of the
input statement is
50 INPUT A,B,C
If this input statement is used in a program, the computer executes
the program in the normal fashion until this statement is encoun-
tered. When the computer finds the input statement, it will display a
question mark on the terminal. After displaying this question mark,
the program cannot proceed until a reply is received from the user.
The user sees the question mark and types the values he wishes to
assign to the variables A, B, and C. The computer then accepts the
three values, assigns them to variables A, B, and C, and continues
the execution of the program.
The input statement can specify as many or as few variables as
needed. However, when the computer types the question mark, the
program must respond by typing as many constants as there are
variables in the input statement.
It is often convenient to have several different input state-
ments scattered through a program. Each input statement can
specify a different combination of variables. In this case, it would be
very easy for the programmer to forget which input statement calls
for which variable. For this reason, programmers usually adopt the
technique of placing a print statement just before the input state-
ment. For example, in the following program, line 20 causes a
message to be printed which clarifies the question mark produced
by line 30. The program looks like this:
20 PRINT "WHAT ARE THE VALUES OF A,B,C,X, AND Y";
30 INPUT A,B,C,X,Y
95
Without the print statement the computer simply prints a
question mark. However, with the print statement the computer
prints:
WHAT ARE THE VALUES OF A.B.C.X, AND Y?
By requiring a reply from the programmer, the input statement
allows the "real-time" input of data. When used with an appropriate
print statement, it also allows two-way communication between the
programmer and the computer. In fact, if enough print and input
statements are carefully used, it can appear that the computer and
the programmer are carrying on an intelligent conversation.
End Statement: The end statement is important because it
must make up the last statement in any program . It consists simply
of a line number followed by the word end . When the computer
encounters this statement, it stops execution of the program.
Chapter 6
Introduction to the ATARI 800
The ATARI 800 is a series of components which function together
with a television set as a single system . The basic system includes :
* Computer Console
* TV Switch Box
* Ac Power Adapter
* Program Recorder and Power Cord
* 2 Instruction Books:
Operators Manual
ATARI BASIC
* 2 Cartridges:
ATARI Educational System
ATARI BASIC LANGUAGE
The software components are the operating system software,
the programs inside the ATARI Educational System, the ATARI
BASIC Language cartridges and, of course , the contents of the two
books .
The basic system may be enhanced in several ways: with
controllers; 8 and 16K RAM memory modules; a printer; floppy
disk drives, and cartridge, disk, and cassette software.
Inside the ATARI 800 Console are the central processing unit
(CPU) and the memory bank containing the operating-system
read-only-memory (10K ROM) module and 8K (8 thousand charac-
ters or "bytes") of user programmable random access memory (8K
RAM), and two expansion sockets for additional RAM memory
97
modules. The Console also holds the keyboard, cartridge slots,
controller jacks, and a serial I/O Port for connecting to peripheral
components.
The TV switch box allows you to change from regular TV
reception to computer display by moving the sliding switch on the
box. The ac power adapter plugs into a normal wall socket and
converts it to the low voltage used by the ATARI 800.
The ATARI program recorder provides software storage in
computer readable form. You may purchase preprogrammed cas-
settes from your ATARI retailer or other software and computer
dealers and you may use any blank, high-quality audio cassette tape
to save programs you write yourself.
UNDERSTANDING SOFTWARE
The ATARI 800 Basic System is very much like an empty sheet
of paper . It has the potential for an unlimited number of applications ,
but that potential remains dormant until you add the software .
The software that accompanies the ATARI computer consists
of programs considerably more complex than those you studied in
the preceding chapter. The foundation programs are supplied in
the operating system ROM module. They activate the keyboard and
the screen display so that you can create pictures and text one
screenful at a time . These programs control the flow of all informa-
tion within the computer.
Usually you add a second level of software to the ATARI 800.
This can be done by inserting a cartridge into the cartridge slot.
This software transforms the ATARI 800 into a special purpose
machine for playing a game , presenting educational material , ma-
nipulating information or entering programs through the keyboard.
The program recorder and optional floppy disk drive provide addi-
tional methods for loading programs into the computer.
ATARI application cartridges contain programs that are per-
manently recorded in a ROM within the cartridge . They control the
computer in machine language , the most intricate level on which to
manipulate the computer. These cartridge programs produce full-
color, animated displays and complex electronic decision-making.
Many entertaining game cartridges are available , and each is de-
signed to be easy to learn but difficult to master.
Other ATARI Cartridges have a more serious purpose . They
are tools for increasing your speed and accuracy in handling words
and numbers. ATARI programmers identify and analyze problems
of interest such as checkbook or mail list management. They then
98
design a generalized solution to each problem, program that solu-
tion in machine language , and record it in the cartridge . When you
insert the cartridge , the ATARI 800 repeats this preprogrammed
solution, substituting your data from the keyboard into its equa-
tions. Although all cartridges operate in the same general fashion,
each cartridge causes the ATARI 800 to use the screen display,
keyboard, and/or controllers in a different way. You will need to
read the instructions which accompany each cartridge for specific
details.
KEYBOARD
The ATARI 800 Keyboard (Fig. 6-1) has alphabetic, numeric,
graphic and screen editing functions which are detailed in the
paragraphs to follow. Most keystrokes produce a visible change on
the display screen. However, there are a few keys which are only
used in combination with others. To investigate the effects of each
key, power up your ATARI 800 without a cartridge in the cartridge
slot and you will see the display pictured in Fig. 6-2. Notice the
square below the A in ATARI. This square is called the cursor. A
cursor is a mark which indicates where the next character you type
will appear on the screen. The ability to move the cursor to any
position on the screen and change the characters being displayed is
one of ATARI 800's most useful features.
A glance at the keyboard (Fig. 6-1) tells you that it closely
resembles that of an ordinary typewriter. In using this keyboard,
remember that each key will repeat its function rapidly if you
depress it for longer than one second.
Special Keys
Pressing either of the shift keys and holding it down while
pressing another key will produce the upper case letter or the
character shown on the upper half of the key , the exclamation mark
or quotation mark, etc.
The control key , Ctrl , functions as a second type of shift . When
it is depressed in conjunction with the escape (esc) key and another
key , a character from a completely new set of characters appears on
the screen. These "graphic" characters can be used to produce
interesting pictures, designs, and graphs either with or without the
ATARI BASIC cartridge . Striking a key while holding down the Ctrl
key will produce the upper-left symbol on those keys having three
functions.
Find the caps/lowr key on the right hand side of the keyboard
99
100
■i^HMilMBlB^
MMMj^^^H^^HHHM
^m
■
ATARI COMPUTER MEMO PAD.'
■
■
1
m^m^mmm^mamm^M
HHH
Fig. 6-2. The "memo page mode."
and press it once. You can then type lower case letters, numbers,
some punctuation marks , and math symbols by pushing single keys .
You can see that the caps/lowr key locks all the alphabet keys
into their alternate character displays. The non-alphabet keys—
those which show two or three characters on the key tops— remain
unchanged. Note that this is not the way the shift lock works on an
ordinary typewriter. Try out the caps/lowr function following the
chart in Fig. 6-3. You will find this feature useful when creating
pictures with graphic characters and when programming in BASIC.
The return key has three functions. First, it moves the printing
mechanism to the left margin and down one line . The ATARI 800
will do this automatically after 38 characters even if the return key
hasn't been pushed. The largest number of characters that will fit on
a single physical line across the screen is 38. However, the com-
puter allows as many as three display lines (116 characters) to be
combined into a single entity called a logical line. Logical lines will
be important when using the screen editor and when programming
in BASIC language.
Second, the return key can be pushed to indicate the end of a
logical line for the computer. At times it will be convenient to push
the return key at the end of each physical line, making it coincide
with each logical line . At other times the end of a logical line will not
coincide with the end of a display line .
Third, the return key activates the computer. The specific
action taken depends on the software that is controlling the com-
puter at the time the return key is pushed.
The clr-set-tab key operates much the same as the tab key on a
regular typewriter. The shift and clr-set-tab keys set a tab stop at
the cursor position. The Ctrl and clr-set-tab keys clear the tab stop
under the cursor. The clr-set-tab key by itself spaces the cursor
101
DO THIS
PRESS jype
H OLD D OWN ffl ABCD . . .
j^3 TYPE
PUSH ABCD...
^ PRESS TYPE
H OLD D OWN p3] ABCD . . .
ctrlI
SEE THIS
Return Key
COMMENTS
UPPER CASE
ALPHABET
LOWER CASE
ALPHABET
CONTROL
GRAPHICS
ON ALL
LETTER KEYS
Fig. 6-3. Upper and lowercase characters.
over to the next tab stop. This key operates on logical lines so you
can set tabs at any position as far as the 116th character.
The A Key switches characters into inverse video. Press it
again to go back to normal display.
The Break Key interrupts the computer while it is busy fol-
lowing instructions. Refer to the cartridge instruction sheet that
came with your computer and to Fig. 6-4 for its exact function.
The Four Keys to the right of the keyboard allow you to select
different starting positions within a cartridge. Each starting posi-
tion is the beginning of a game or an application stored within a
single cartridge. Push the system reset key to stop the computer
and start from the beginning of the next game or application. Push
the option key to choose among the variations possible within a
game or application. After you have made your choices with the
select and option keys, push the start key to begin the action. More
complete instructions are provided with each cartridge.
Edit Features
In addition to these special function keys, there are keys that
allow immediate editing capabilities. These keys move the cursor
and modify the display. They are used in conjunction with the shift
and ctrl keys.
The following key functions are described in this section.
CTRL+
CTRL*-
CTRL CLEAR
SHIFT CLEAR
CTRL INSERT
CTRL DELETE
SHIFT INSERT
-ill
BREAK
102
CTRL i SHIFT DELETE ESC
CTRL<«- DELETE
Homing the Cursor. Pressing the shift and clear or Ctrl and
clear keys simultaneously erases all characters on the screen and
moves the cursor to the home position at the upper left corner of the
screen.
Moving the Cursor. To move the cursor, press the Ctrl key
and the appropriate arrow key at the same time .
CTRL 4 : Moves cursor up one physical line without changing
the program or display.
CTRL-*- : Moves cursor one space to the right without dis-
turbing the program display.
I4J:I1 §^JJg| Inserts one character space.
BH liUIA^ Deletes one character or space.
1 Stops temporarily and restarts screen display with-
out "breaking out" of the program.
2 Rings buzzer.
3 Indicates end-of-file.
Keys Used With ffiSSS
B.-l!llaM H,'Hd:H Inserts one physical line.
Deletes one physical line.
WHMSM'H-M Returns screen display to tipper-case alphabetic char-
acters.
Special Function Keys
Stops program execution or program list, prints a
READY on the screen, and displays cursor.
Allows commands normally used in direct mode to
be placed in deferred mode; e.g., In direct mode,
IBB tTI JJ clears the screen display. To clear the
screen in deferred mode, type the following afte r the
program line number. Press ESI then press BZ3S
and BtllJJ:B together.
PRINT " (jgjl BUI *3T3%B "
Fig. 6-4. Keys used with the control keys.
103
CTRL i : Moves cursor down one physical line without chang-
ing the program or display .
CTRL-*-: Moves cursor one space to the left without disturbing
the program or display .
Like the other keys on the ATARI keyboard , holding the cursor
control keys for more than Vz second causes the keys to repeat.
When the cursor is placed on top of a letter, that letter is shown in
"inverse video" on the screen. When the cursor is moved away from
the letter, the letter returns to its normal state. If the cursor is
placed on top of a character and then another key is pushed , the new
character will replace the original one .
Line Insert Function: Press the shift and insert keys simul-
taneously to create a space for a new line. The logical line that
contained the cursor, and all lines below, it will be moved down one
line. Be aware that any information on the bottom line of the screen
will be lost.
Character Insert Function: Press the control and insert
keys simultaneously to a space for a new character. The character
under the cursor will be moved to the right. The rest of the line will
also shift to the right. The cursor remains on the space which is now
available for a new character.
Character Erase Function: Pressing the delete back s key
erases each character as the cursor moves back one space at a time .
The total length of the line remains unchanged.
Line Delete Function: Pressing the shift and delete back s
keys simultaneously removes one whole logical line. If there are
lines below the one that was deleted, they will all move up one line
leaving a new blank line at the bottom of the screen.
Character Delete Function: Pressing the Ctrl and delete
back s keys erases the character under the cursor by moving all the
characters to the right of the cursor one space to the left. The lines
become shorter.
The Esc (escape) Key disables the cursor control move-
ments and prints a graphic character instead. For example, press
the esc key; then hold down the Ctrl key while pressing the delete
back s key. Instead of the text moving to the left, you will see a
special graphics character displayed. This function will prove very
useful when you begin programming in BASIC. The characters
produced in this manner are shown in Fig. 6-5.
The A Key switches characters into inverse video. Press it
again to go back to normal display.
The Break Key interrupts the computer while it is busy
104
DO THIS
PUSH PUSH
SEE THIS
PUSH PUSH SIMULTANEOUSLY
PUSH PUSH SIMULTANEOUSLY
Special Computer Keys
TheQkey switches characters into inverse video Press it again to go back to normal
display
1I:IJV interrupts the computer while it is busy following instructions Refer to the
cartridge instruction sheet for its exact function.
Fig. 6-5. Keys producing graphics.
following instructions. Refer to the cartridge instruction sheet that
came with your computer and to Fig. 6-5 for its exact function.
PROGRAM RECORDER
The ATARI program recorder is used with a cassette to hold
blocks of software too large to be maintained in cartridge form.
Programs, recorded on magnetic tape, are copied by the computer
from the tape into RAM memory. You can run or modify these
105
programs by entering instructions through the keyboard. You can
also type your own programs into memory , and then store them on
tape for later use or modification .
The ATARI program recorder resembles an ordinary audio
cassette tape recorder. Its playback and recording levels have been
permanently set at the correct volume for use with the ATARI
Computer.
The instructions with each program cassette type on the
keyboard to have the computer begin to load the tape. After the
program is completely loaded into the computer, the tape will stop
automatically. Press the stop-eject button on your recorder to turn
off the motor. Now type a command or press the computer system
key labeled "start"— whichever is specified on the instruction
sheet— to begin using the program.
LEARNING TO PROGRAM THE ATARI 800
With the large array of preprogrammed cartridges available for
the ATARI 800, one might find it difficult to imagine why it is
necessary to learn how to program the computer. Once you become
involved in computer use, you will quickly find that you'll have
numerous uses for the computer for which no preprogrammed
cartridges are available. You can, of course, hire a programmer to
work the problem out for you, but this can run into the money and
cost you a pretty penny. So, it's best if you learn to work out the
programs for yourself.
Even if you have no practical use for computer programming,
you may find that learning to write programs in BASIC for your
ATARI 800 is an exciting and valuable experience . Programming
sharpens your skill in thinking, in analyzing problems, and in de-
vising step-by-step solutions. It deepens your understanding of
computers in general, and no one can deny that computers are
becoming a major force in modern society. A knowledge of pro-
gramming makes you a more informed consumer and citizen who no
longer accepts "It was the computer's fault" as an excuse for bad
management.
But perhaps the most important reason to learn to program is
that it is fun. Start by instructing the computer to draw pictures and
to print verbal messages on the display screen. Soon you will be
choosing more and more complex tasks for your ATARI 800 and will
be enjoying the challenge of designing programs which allow the
computer to do your bidding.
As mentioned in an earlier chapter, good computer programs
106
are usually created in three stages— design, coding and debugging.
During design you choose a task for the computer and analyze it into
its component parts. During coding you translate these parts from
their English or mathematical form into a computer language , in this
case ATARI BASIC. Next you type your coded program into the
ATARI 800 computer. As each line is typed, ATARI BASIC will
check it and report any mistakes in coding. After you have corrected
these mistakes in coding, you can try to run your program. In other
words, you can direct the computer to follow the set of instructions
you have given it. Often you find you have made an error some-
where. The ATARI 800 may succeed in running your program, but
the result is not exactly what you wanted. Perhaps you have made
an error in design and need to go back and plan your program more
carefully. At other times the computer will tell you that it can't
follow your instructions as given because they contain logical or
grammatical errors. You have made an error in coding or typing. At
the third stage, debugging, you find and correct all of your remain-
ing errors. You continue to run and debug your program until the
ATARI 800, under the control of your program, produces the re-
sults you desire.
Note that no computer actually "solves problems" or "answers
questions" by itself. Using your design, the computer performs the
instructions you have given it. It mechanically produces a "solution"
to a problem whenever you run the program.
As mentioned in Chapter 5, BASIC (Beginners All-Purpose
Symbolic Instruction Code) was invented so that people could learn
to write programs quickly and easily. To you, the user, the BASIC
language is a set of rules stated in English which tells you how to
give the computer the instructions it needs to do your bidding. To
the computer, BASIC is the same set of rules written in machine
language. The rules enable it to translate your BASIC instructions
into action. We call this machine language program that "translates"
BASIC into machine language the BASIC language interpreter. It is
contained in the ATARI BASIC Language Cartridge . The program
which you write is called the BASIC source program. You enter
your source program into the ATARI'S random access memory by
typing it on the keyboard while the BASIC cartridge is in the
cartridge slot. The ATARI uses the operating system programs (in
the operating system ROM), the BASIC language interpreter (in
the cartridge), and your BASIC source program (typed on the
keyboard or loaded from cassette and stored in RAM) in order to
follow the instruction you have written in your program.
107
WRITING BASIC SOURCE PROGRAMS
This section will give you a brief introduction to actually
programming the ATARI 800 computer- in ATARI BASIC. You
were given a brief introduction to fundamental BASIC programming
in an earlier chapter, but here you will actually start to press keys on
the keyboard and see the results on the screen. Follow the instruc-
tions exactly , but don't expect to understand all of them at this time .
You'll eventually have a good understanding of programming, but it
will have to come with time and experience. If you are a program-
mer experienced in using other forms of BASIC, the following
paragraphs will give you insights into ATARI BASIC specifically.
Remember, however, there is a great deal more to learn than is
presented in this chapter.
First of all , let's explore the use of nine BASIC commands : run ,
break , return , dim , print , input , list , if . . . then , and goto . Start out
by inserting the BASIC cartridge and powering up . In the upper left
hand corner of the screen, you'll see the word ready. This is the
BASIC prompt. It is a message from BASIC to you telling you that
the computer is waiting for a command. You'll also see a small
square mark directly beneath the word ready. This mark is the
cursor. It tells you where the next character will be printed.
Since ATARI BASIC language can only read upper case let-
ters, press the shift and caps/lowr keys. This locks all letters into
upper case. Now type an English sentence
COMPUTER, ARE YOU AWAKE?
and push return. The screen will now appear as shown in Fig. 6-6.
Yes, ATARI 800 is awake. It is sending you a prerecorded
message saying that you have typed in, or entered, a line of charac-
ters which is not in its list of correct BASIC language codes. You
may find out more about your mistakes in the chapter on Error
Messages in ATARI BASIC in your ATARI owners' manual . Before
you look at this chapter, however, try entering the line again with
these changes. Type the line exactly as shown, including the word
print and the quotation marks:
PRINT "ATARI 800, ARE YOU AWAKE?"
Be meticulous when you type. The computer cannot guess what you
meant to include nor can it ignore extra characters. The computer
will display each character on the screen as you type. The line above
108
DO THIS
TYPE
COHPUTER. ARE YOU AWAKED
PUSH
SEE THIS
COMMENTS
1 . BASIC prompt - This will disappear off the
top of the screen as new lines are added
at the bottom.
2. You typed this line.
3. This is an ERROR MESSAGE from
BASIC telling you that your source pro-
gram cannot be interpreted.
The light and dark colors are reversed at
the first illegal character.
4. BASIC prompt
5. The cursor again.
Fig. 6-6. The error message.
is correct BASIC code . Now push the return key and the new screen
should appear as shown in Fig. 6-7.
If your screen display doesn't look like the one in Fig. 6-7,
check the display to make sure you have copied every character
exactly. Be sure to start your line with the cursor at the left margin.
When you have found your mistake push the return key and try
again.
Play around with the print command for a few minutes. You
may put any characters you like inside the quotation marks including
all the graphic and control characters described earlier in this
chapter. Experiment with the cursor controls and with logical lines
of up to 116 characters. What happens if you forget to put in the
quotation marks? Try it and see.
Occasionally you may "lose control" of your computer by
inadvertantly commanding it to do something you didn't anticipate.
If this happens, press the break key. If you have been using a
program the computer should display
STOPPED AT LINE 10 (or some other number)
If the break key doesn't work, press the system reset key. The
initial (blank) screen will be displayed.
You can also use the print command to turn your ATARI 800
into a calculator. Type the following on the keyboard.
PRINT 45782 + 11111
109
DO THIS
TYPE
PRINT ATARI 800. ARE
YOU AWAKE?'
PUSH
I RETURN |
SEE THIS
1.
2.
3.
( \
READY
PRINT 'ATARI 800, ARE YOU AWAKE?"
ATARI 800, ARE YOU AWAKE
^ )
Fig. 6-7. Printing in the direct mode.
and push return. The display should appear as shown in Fig. 6-8.
The ATARI 800 evaluates expressions in the same way you
were taught to do it in elementary school. Everything inside
parentheses ( ) will be done first. Then exponentiation (A) will be
done. Exponentiation involves multiplying a number by itself a
DO THIS
TYPE
PRINT 45782 + 11111
PUSH
I"returnI
SEE THIS
(
A
1.
READY
2.
PRINT 45782 + 11111
3.
56893
4.
READY
J
Fig. 6-8. Using the computer as a calculator.
110
specified number of times. For example, 5 A3 means 5 times 5
times 5 and is equal to 125. You will often see this expression
written 5 3 . It is read "five raised to the third power". Type the
exponentiation symbol on the computer by pressing the shift key
and the key with the symbol A on it (The A symbol will be found in
the upper right-hand corner of a key near the right side of the
keyboard.)
All multiplication (*) and division / is done next. Addition +
and subtraction - are performed last. If you have forgotten that the
order in which calculations are done is important, try a few prob-
lems. You will find that (4+6)/5 = 2, while 4+6/5 = 5.2, and 4/5+6
= 6.8.
The ATARI 800 will print any whole number value in the range
-999999999 to 999999999. It will express fractions and numbers
outside this range in scientific notation as a decimal number be-
tween one and ten times a power of ten . For example , if the value of
your expression is 12,345,678,909 the ATARI 800 will write it as
1.23456789E + 10. E + 10 means you must move the decimal point
ten places to the right to obtain the original number. You read
this number as 1.23456789 times ten to the tenth power
(10,000,000,000).
You can enter any expression and the ATARI 800 will do the
arithmetic. Remember that the BASIC language does not tell you
the correct expression to use to solve number problems. You must
figure out how to calculate interest payments , sales commissions ,
expected time of arrival, or whatever you want to know. BASIC
does have a large repertoire of arithmetic, algebraic, and trig-
onometric functions available, but you, the programmer, must tell
the computer how to combine them to produce meaningful results.
You will find a complete discussion of BASIC language arithmetic in
a later chapter.
Thus far, we have been using ATARI BASIC language in the
direct mode; that is, the ATARI 800 follows your command as soon
as you give it and then forgets about it. In the program mode, you
may give the computer as many as about two hundred lines of
instructions. Each line is then stored until the run command is
entered. Then the computer follows one instruction after another
until the whole task is completed.
Although most BASIC commands can be given in direct mode,
only a few of them are useful to the beginner. The run command is
almost always used in direct mode. It is used to start a program at
the beginning. It is typed as a three letter sequence in upper case
111
only. No action occurs until you press the return key. This key
signals the computer to read what you have typed and to execute the
entire series of instructions. Pressing the break key stops the
program from running and displays the cursor. Break and return are
the only single key commands in BASIC . All others are typed as a
series of letters followed by the return key .
If you wish to enter a program into the ATARI 800 using the
program mode, start each line at the left margin of the screen with a
line number. You may number your lines with any whole numbers
between one and 32767. You may enter program lines in any order.
However, the computer will rearrange them and execute them
starting with the line with the smallest number and proceeding to
the next higher numbered line until all instructions have been
followed. Most BASIC language programmers number their lines
by tens so that they have nine line numbers available in case they
wish to add new lines between the original ones.
To get started, power down and up once again. This will clear
out your RAM memory. Then print:
10 PRINT "WIZARD, ARE YOU AWAKE?"
Continue by pushing return and then typing run; then press return
again. The display should appear as shown in Fig. 6-9. You have just
entered and run a BASIC program!
To edit any line of BASIC code, use the display control keys.
Position the cursor over the character you wish to change and make
the corrections within a logical line. When the line is correct, press
the return key . The ATARI 800 will put the corrected line in place of
DO THIS
TYPE
'10 PRINT "WIZARD. ARE YOU AWAKE?'
SEE THIS
PUSH
I— I 1.
PUSH
COMMENTS
1 . Here is your one line program:
2. The computer found your stored instruction
and followed it.
3. After completing its task, the computer sig-
nals you with the BASIC prompt.
Fig. 6-9. Printing in the deferred mode.
112
the original one in RAM. To remove a whole line, type its line
number and press the return key. For practice, replace the word
"Wizard" in line 10 with your own name. Be sure to make your
changes in the numbered line 10, not the line displayed after "run ."
List is the command that makes the computer display your
BASIC source program. Any time you wish to see the instructions
your computer is following, press break, type list, and press the
return key. Note that you may use the break key to interrupt the
computer even if it is running a program or calculating. All other
commands must be given only after the cursor is displayed. Com-
mands must be typed in upper case or you will get an error message .
Now add the following lines to your program. Remember to press
the return key before beginning a new line that starts with a line
number. Be sure not to leave out the colons.
5 DIMA$(10)
20 Input A$
30 IF A$ = "YES" THEN PRINT "YOUR PROG
RAMMING CAREER HAS BEGUN.":GOTO 60
40 IF A$ = "NO" THEN PRINT "TECHNOLO
GY MAY PASS YOU BY . . . ":GOTO 10
60 PRINT "THIS PROGRAM HAS ENDED."
You should know that BASIC ignores blank spaces unless they
are inside quotation marks so you can leave them out when you need
to save space. However, do put them in when you can so your
listings will be easier for people to read.
Run this program and answer the question "Are you awake?"
several times. Type your answer after the ? and then push the
return key. Run the program several times more. Try responding
Yes ; YES ; yes; No; and maybe. What happens when your answer is
neither 'YES" nor "NO"? The program should print the message in
line 60 and then end.
To understand what the computer is doing, examine the pro-
gram line by line. Line 5 sets aside a place in the computer's
memory for your answer to the question in line 10. Line 10 has the
command print "something." This something that you put be-
tween the quotation marks is called a string constant: string be-
cause it is a string of letters, numbers, and/or graphic characters,
and constant because it will remain the same every time you run this
program.
Line 20 has the command "input something". This means:
113
"Computer, wait until something is typed on the keyboard. Show
whatever is typed on the screen and store it in a space in RAM
memory labeled A$. When the return key is pressed, go on to the
instruction with the next higher line number." A$ (read A string) is
called a string variable because it is a string of letters, numbers,
and/or graphic characters which will be different every time you run
this program. Each string variable within a single program must
have a different label. Many labels are available in BASIC, but for
now, limit yourself to A$ through Z$. Line 5 gave us space to store
ten characters in A$. If we expected a long answer we could save
more memory for A$ by using a large number within the paren-
theses.
Line 30 has if . . . then print "something" : GOTO 60. When the
condition following if is met, that is, when the computer finds the
letters Y-E-S stored in the place in memory labeled A$, the instruc-
tions in the rest of the line are followed. It prints "Your Program-
ming career has just begun." The computer encounters the colon (:)
next. This tells it that another command is coming. The GOTO
command says "skip down to line 60 and ignore the lines in be-
tween."
When the condition is not met, that is , when the computer finds
that anything besides Y-E-S has been entered at line 20, the rest of
the line is ignored and the computer goes on to the next numbered
line, in this case, line 40.
Line 40 operates the same way as line 30 does. If anything but
N-0 has been entered at line 20, its condition isn't met, and line 40
doesn't print anything. The computer just goes on to the next
numbered line which is line 60. Line 60 prints its message, and
since there are no more lines, the program ends and ready is
displayed. If N-0 has been entered at line 20, all of the line 40 would
be executed . The message in line 40 would be printed and program
control would jump back to line 10. The program would begin over
again.
Suppose the programmer wants to demand an answer of "YES"
or "NO" before the program will end. The computer must be
programmed to print a message whenever something other than
"YES" or "NO" has been entered. After this message, the question
should be repeated on the display screen. Try to figure out what line
to add to make the computer do this. There are many ways, but one
solution would be:
50 PRINT "YOU MUST ANSWER 'YES' OR 'NO'
TO GO ON.":GOTO 10
114
Enter this line. List and run this revised program several
times. To anticipate what the display will look like, pretend you are
the computer and follow the program. Remember that computers
are machines which blindly stick to their programs no matter how
nonsensical the results may be. This is why the design stage of
programming is so important. It is up to you, the programmer, to
plan each display the user will see, to anticipate what the user will
type in response to that display , and to tell the computer what to do
with every response.
You can use the previous format to code an unlimited number of
dialogue-type programs. You will need to change the string con-
stants and occasionally rearrange the GOTO's. Here is another
example ... a type of quiz .
10 DIMN$(100)
20 DIMA$(20)
30 DIMP$(20)
110 PRINT "THIS IS THE OCEANS PROGRAM."
120 PRINT "HELLO, WHAT IS YOUR NAME";
130 INPUT N$
140 PRINT "OK, ";N$;
150 PRINT ".NAME AN OCEAN THAT BEGINS WITH P."
160 INPUT P$
170 IF P$ = "PACIFIC" THEN PRINT "PERFECT.":GOTO
190
180 PRINT "THAT ISN'T THE ONE WE ARE LOOKING FOR.
TRY AGAIN."; GOTO 150
190 PRINT "NOW NAME ONE THAT BEGINS WITH A."
200 INPUT A$
210 IF A$ = "ATLANTIC" THEN PRINT "YOU'RE TOO
GOOD, "N$;" . NOW GIVE SOMEONE ELSE A
TURN.":GOTO 120
220 PRINT "TRY AGAIN. REMEMBER SPELLING
COUNTS!": GOTO 190
The display on the screen will appear as shown in Fig. 6-6 for
this particular program. See if you can follow the program and the
answers on the screen. Does it make sense?
EDITING YOUR PROGRAM
To perfect your program, you will want to use the keys de-
scribed under "Edit Features" earlier in this chapter. When you are
using these keys, remember that the keyboard and display are
115
Fig. 6-10. A question and answer program.
logically combined for a mode of operation known as screen-editing.
Each time a change is completed on the screen, the return key must
be pressed. Otherwise, the change is not made to the program in
RAM.
Example: 10 REM PRESS RETURN AFTER LINE EDIT
20 PRINT :PRINT
30 PRINT "THIS IS LINE 1 ON THE SCREEN."
To delete line 20 from the above program, type the line number
and press the return key. Merely deleting the line from the screen
display does not delete it from the program.
TRANSFERRING PROGRAMS TO AND FROM CASSETTE TAPES
Now that you have a BASIC program entered into the com-
puter, and you know that it runs, you may want to save it on tape.
Once you have a copy of the program on tape , you will never have to
type that particular program again. When you want to change your
program, you can load your first version from the tape; edit the old
lines and add new ones; then save the new version. The copy in the
computer disappears each time you turn off your computer or load
116
another program, but the copy on the tape will be available until you
choose to erase it.
Set up your program recorder according to the instructions
provided by the manufacturer. See Fig. 6-11. If you already have a
program in the computer, be sure not to shut the power off at any
time. If you have not yet written a BASIC Source Program, write
one.
To transfer a program to tape:
1. Insert a blank cassette tape into the program recorder with
the recording surface toward you and the label so that you can
read it.
2. Push the rewind button and wait until the tape stops.
3. Push the tape-counter reset button until it reads 0000.
4. Push the stop-eject button once.
5. Type CSAVE on the computer keyboard. Then press the
return key. You should hear two beeps.
6. Push the record and play buttons simultaneously. Now
push the return key on again. You will hear a series of tones
indicating that the recorder is now being controlled by the
computer. The recorder will erase the beginning of the tape
surface for eighteen seconds; write the introductory header
needed by the computer; copy your program onto the tape;
then stop.
Fig. 6-1 1 . Connecting the cassette recorder.
117
7. It is always good programming technique to create a
backup copy of each program you wish to save. ATARI re-
comends that you store one program on each cassette and
keep a backup on a separate cassette— just in case!
8. If you are planning to store more than one copy of the
program on the tape, you may make your backup by repeating
steps 5 and 6. Be sure to write down the starting tape-counter
number for your backups as well as for your original pro-
grams.
9. Push the stop button on the program recorder.
10. Finally, write the name of your new program and its tape-
counter number on the cassette label and on a page which you
keep in the binder with your manuals.
To load a program from tape to the computer.
1. Insert BASIC source tape into the program recorder.
2. Rewind tape to the beginning and press the stop-eject
button.
3. Press the tape-counter reset button until it reads 000. If
you have put more than one program on a single tape, advance
the tape to the number where your program starts.
4. Type CLOAD on the computer keyboard. Then press the
return key. You will hear one beep.
5. Push the play button on the program recorder. Then push
the return key again. You will hear a series of tones as your
program is loaded.
6. When the tape stops, your program has been transfered
from the cassette tape to the computer.
7. Push the stop-eject button on the program recorder.
We have covered quite a lot of material in this chapter so don't
be discouraged if you're somewhat confused at this point. Many
people are inexperienced in the kind of logical thinking required to
write programs, so allow yourself plenty of time to become com-
fortable with the step-by-step nature of the computer, and the
sometimes infuriating attention you must pay to detail. Remember
that inexperience does not mean inability. There are a tremendous
number of new and sophisticated concepts presented in this book.
You will want to read it many times and keep it handy so that you can
look up details when you forget them.
The chapters that follow will give you more experience in
BASIC programming on the ATARI 800. They will include methods
of using graphics and sound.
118
Chapter 7
Optional Peripherals and Software
The ATARI 800 can be customized by adding components that are
appropriate for the tasks you have at hand. By choosing a particular
combination of preprogrammed software, controllers, memory
modules, and peripheral components, you can completely change
the character and capacity of the machine.
8K COMPUTER SYSTEMS
The ATARI 800 basic system contains 8K of random-access
memory and the ATARI 410 program recorder. This system config-
uration will accommodate all of the preprogrammed cartridges and
cassettes which make up ATARI'S 8K library . Some of the software
in the 8K library will require the use of hand held controllers which
are available from ATARI retailers.
In addition to the preprogrammed 8K library, the BASIC lan-
guage cartridge may be used in conjunction with the 410 program
recorder and any high-quality audio cassette to create and store an
unlimited number of programs that you may want to write yourself.
The ATARI BASIC language offers you the opportunity to use
sophisticated graphic displays, four- voice sound, and input from the
controllers of your choice in programs limited only by your imagi-
nation.
THE PRINTER
The ATARI 820 printer may be added to any ATARI 800
119
system. Some programs in the 8K library will offer the option of
printing program results as well as displaying them on the screen.
The 820 is a high-resolution, dot-matrix, impact printer which uses
standard 4-inch roll paper and will output up to forty characters per
second. Your printer should be connected in a "daisy chain" series
between the serial jack labeled PERIPHERAL on the side panel of
the ATARI console and the program recorder. See your manual for
details.
16K COMPUTER SYSTEMS
The basic ATARI 800 system comes with one 8K random-
access memory module installed. This module contains approxi-
mately 8,000 storage cells to use . The capacity of the computer may
be expanded to enable you to use longer programs by inserting
additional RAM memory modules into one or both of the empty
sockets in the memory bank. These modules may be purchased in
8K and 16K versions. The 8K version is ATARI part number
CX852. The 16K version is part number CX853.
These additional memory modules may be inserted in any
combination (see Fig. 7-1), except that the 10K ROM must remain
in socket 0. Also, socket 1 must be filled first; then socket 2, and
finally socket 3. Note that the ninth option, 48K of memory, dis-
ables the cartridge slots and should only be used after gaining some
experience operating the computer.
The memory bank is located under the ribbed top cover of the
console. You may install modules yourself by opening the cover and
arranging the modules in one of several configurations as shown in
Fig. 7-1 . To install these modules, first, turn the power off using the
main power switch, and open the cartridge door. Next rotate the
two black clamps outward as far as they will go. Lift up the front
edge of the cover slightly and slide the entire hinged door and ribbed
top cover toward you. Inside the memory bank you will see four
module sockets, two of which are already occupied by the operating
system 10K ROM and one 8K RAM module. The operating system
10K ROM must remain in the front socket. The other three sockets
are available for expanding the computer's RAM.
When inserting modules, press firmly on both sides and push
straight down. The ATARI 800 may then be reassembled by slip-
ping the back of the ribbed cover into place first. The two metal tabs
on the underside of the cover fit into two slots at the back edge of the
console. Shut the front edge of the cover and replace the blank
120
16K TOTAL 24K TOTAL . 32K- K '
i S
a s
8K TOTAL 16K TOTAL
24K TOTAL
LOTAL 40K TOTAL 48K. TOTAL :
Fig. 7-1. The ATARI console.
plastic clamps by rotating them forward. Close the cartridge slot
door and power up again.
CONTROLLERS
There are several different controllers used with the ATARI
800. Each of them can be attached directly to the computer or to
external mechanical devices so that outside events can be fed
directly to the computer for processing and control purposes.
Paddle: A paddle consists of a knob that can be turned to send
a number between 1 and 228 to the computer. The number in-
creases as the knob is rotated counterclockwise. This number can
121
be used with other functions or commands to "cause" further actions
such as changes in sound or graphics. For example, you can use the
statement IF PADDLE(3) = 14 THEN PRINT "PADDLE AC-
TIVE." The ATARI console can control eight paddle controllers
numbered zero through seven from left to right.
Paddle Trigger (PTRIG): The paddle trigger is a button on
the paddle . You can use the PTRIG statement to determine whether
the button is pressed (returns a value of 0) or not pressed (returns a
value of 1) on a particular paddle (0-7). For example, you can use the
statement IF PTRIG (3) = THEN PRINT "BOMBS DROPPED!"
Joystick: Many game cartridges available for the ATARI use
"joystick controllers to move images on the screen. All four joy-
sticks in a set are identical and can plug into any of the controller
jacks provided on the console . Each joystick has one button and a
stick which can be pointed in eight possible positions. Hold the
joystick with the button in the upper left-hand corner and push the
top of the stick in the direction that you want to move the object on
the screen. Always consult the instructions that came with the
cartridge to determine whether or not joystick should be used and, if
so, what each position means.
If you wish to use the joystick in programs you write yourself,
use the stick command just as you used the paddle command. Each
joystick position will return a different number as shown in Fig. 7-2.
The joystick controllers are numbered from 0-3 from left to right.
First controller STICK(O)
Second controller STICK(l)
Third controller STICK(2)
Fourth controller STICK(3)
Stick Trigger (STRIG): The button on the joystick is the
stick trigger. You can use the STRIG statement for the stick trigger
in the same way you used the PTRIG statement for the paddle
trigger. You can also use the STRIG statement to evaluate the
status of a key on the keyboard that you have designated as a
controller.
THE ATARI 810 DISK DRIVE
The ATARI 810 disk drive provides fast, reliable data storage
and has the capabilities to:
1. Store programs on diskette.
122
Fig. 7-2. Joystick controller movement.
2. Retrieve programs from diskette.
3. Create and add to data files needed by programs.
4. Make copies of disk files.
5. Erase old files from a diskette.
6. Load and save binary files.
7. Move files to and from memory, screen, diskette, printer,
and any new peripherals that ATARI may introduce.
Each disk drive contains a microprocessor with its own
software in addition to the hardware necessary for the magnetic
head to move back and forth "across" a floppy diskette. The ATARI
800 with 16K of RAM can accommodate up to four ATARI 810 disk
drives, and each will operate independently of the others.
ATARI diskettes are thin, circular mylar sheets covered with
an oxide similar to that used on recording tape . They are protected
by a special, black jacket which keeps them from being bent,
scratched, or contaminated. See Fig. 7-3.
Before writing on a blank diskette, the surface must be "or-
ganized" so that the disk operating system (see the next section)
will know where the information is located. This is accomplished by
formatting a diskette into tracks and sectors . The diskette is logically
divided into 40 tracks with 18 sectors per track. Each of these
123
ATARI Label .
Writ«-Prot»ct
"Notch
Spindlt Hoi*
Timing Hol»
Read/Writ*
Are*
Fig. 7-3. An ATARI diskette.
single-density diskettes has a total of 720 sectors on which informa-
tion may be written.
Eleven of the sectors are allocated by the DOS for "special
duty" so they are not available to you.
1 sector is used for the boot.
8 sectors are used for the directory.
1 sector is used for the volume table of contents.
1 sector (number 720) is not addressable and so is unused.
11 TOTAL
Each of the remaining 709 sectors can store 128 bytes of
information, 3 bytes of which are used for overhead. That gives a
total byte capacity per single-density diskette of 88,625 bytes!
DISK OPERATING SYSTEM
DOS (pronounced doss) is an acronym for disk operating sys-
tem. It is an extension of the ATARI operating system (OS) that
allows interfacing with a disk drive so that information can be
passed between the diskette and the computer memory (RAM) .
The operating system contains two main parts: a disk utility
package (DUP) and a file management subsystem . When the system
is energized, it executes a bootstrap loader (self loader) that brings a
special file called DOS SYS into RAM and begins executing the
124
initial code in that file. DOS SYS contains both the file management
subsystem and the disk utility package.
When DOS is loaded into the computer RAM, it occupies a
special area in RAM that does not interfere with the memory
locations allocated for BASIC or assembly language programs. The
memory map in Fig. 7-4 shows the RAM locations occupied by the
DOS. After the disk drive system has been booted and the DOS SYS
file is loaded, the ATARI operating system turns control of the
system to the cartridge. If no cartridge has been inserted, OS gives
control of the system directly to the disk utility package (DUP).
The executive program in the DUP allows you to display the
DOS menu which lists the commands available to you . For example ,
DELETE FILESPEC is menu selection D. It then executes the
selected utility. The DUP program also allows easy access to the
file management subsystem (FMS) without your having to under-
stand the logical structure of FMS.
ADDRESS
DECIMAL HEXADECIMAL
69939 FFFF
EOOO
CONTENTS
OPERATING SYSTEM ROM
10879
9896
2A7F
2680
DISK OPERATINO SYSTEM (2A7F-700)
DISK I/O BUFFERS (current DOS)
9889
4864
267F
1300
DISK OPERATINO SYSTEM RAM
(currtnt DOS >
4863
1792
13FF
700
FILE MANAGEMENT SYSTEM RAM
'current DOS 1
1791
1936
6FF
600
FREE RAM
1191
1021
47F
3FD
OPERATINO SYSTEM RAM (47F-300)
CASSETTE BUFFER
999
960
3E7
3C0
PRINTER BUFFER
911
296
IFF
100
HARDWARE STACK
299
213
FF
04
PAOE ZFJ»0
FLOATING POINT (ui*d by BASIC)
211
210
D3
03
BASIC or CARTRIDGE PROGRAM
209
308
Dl
DO
FREE BASIC RAM
207
203
CF
Ci
FREE BASIC ind ASSEM3LER RAM
202
176
128
CA
BO
FREE ASSEMBLER RAM
ASSEMBLER ZERO PAOE
BASIC
ZERO PAOE
Fig. 7-4. Memory map (partial).
125
File Management Subsystem
This system provides a simple way of storing data on a diskette
by putting a logical structure on top of the formatted diskette.
Because of the file manager program, it is not necessary to keep
track the number of the sectors a program occupies, which sectors
they are , or how to find a particular file . FMS rel ieves the user of all
that responsibility.
Operations on a file, such as open, close, put, and get are also
controlled by the FMS. In addition, it defines the subfunctions
displayed on the DOS menu and are accessed by the DUP. The
subfunctions that are not defined by FMS are binary load, binary
save, run at an address, run cartridge, copy file, duplicate file and
duplicate disk.
The FMS organizes files using filenames you have assigned to
your files.
The disk directory contains a list of all the files on a diskette.
On demand, it displays the filename, the extender, and the number
of sectors allocated to that file . It will either display a partial list or a
complete list depending on the parameters entered. Wildcards can
be used in the parameters.
The ATARI DOS recognizes two "wild cards" which can be
substituted for characters in a filename . They are represented by
the special characters ? and *. The first, ?, is used in place of any
single valid character. If there are 25 files on a diskette and you want
to display a list of those five-letter file names that begin with PROB
and have the extender (ending) .BAS, you would type PROBP.BAS.
This wild card can only be substituted for a single character. To
substitute for a variable number of characters, there is another,
more flexible wild card.
The * stands for any valid combination of characters in a
filename or an extender. The following examples illustrate the use
of the *.
*.BAS will list all the program files on a diskette in
drive 1 that end in .BAS.
D2:*. * will list all the program files on the diskette in
drive 2.
PRO*. BAS will list all the program files on the diskette in
drive 1 that begin with PRO and have .BAS as
the extender.
126
A program may be loaded from the diskette using a wild card in
the file name if there is no more than one file to which it is
applicable.
The ATARI 810 also has the capabilities to copy files. For
example, if you desire to copy a file from one diskette in drive 1 to a
second diskette in drive 2, this can be easily done. You can also
create a backup copy of a file on the same diskette by using the same
filename with a different extender, or even by using a completely
different filename.
BASIC COMMANDS USED WITH DISK OPERATIONS
BASIC commands used to store and retrieve files are load,
save, list, and enter. Other BASIC commands used with disk oper-
ations are note, point, and DOS.
L0AD(L0.)
Format: LOAD filespec
Example: LOAD "D1JANINE.BRY"
This command causes the computer system to load the file
from the disk drive specified into the RAM. (Note here that it loads
the tokenized version of the program. The tokenized version is
shorter than the untokenized version in that, when recorded, this
version contains shorter interrecord gaps. However, when a
tokenized version is loaded, it also loads the program's symbol
table. If the program is altered or deletions are made, the symbol
table is NOT changed. This means that all variables which are.
defined in the original program still exist in the symbol table.
Therefore, it is recommended that load and save be used only when
saving a program is its final form .) When loading a file from drive 1,
it is not necessary to specify the drive number.
The load command can also be used as a BASIC statement to
"chain" programs . If you have a program that is too big to run in the
available RAM, you can use the load statement as the last line of the
first program. When the program encounters the load statement, it
will automatically read in the next part of the program from the
diskette. However, the second program must be able to stand alone
without depending on any variables, and the like from the first
program.
SAVE(S.)
Format: SAVE "filespec"
Example: SAVE "D1JANINE.BRY"
127
This command causes the computer system to save a program
on a diskette using the file name designated in the command. Save is
the complement of load and stores programs in tokenized form.
LIST(L)
Format: LIST "filespec"
Example: LIST "D: DEMOPR.INS"
When a disk drive is specified, the list command causes the
computer system to move the program currently in RAM to a file on
the diskette using the filename specified in the command. This
command unlike save, saves the file in untokenized format.
ENTER(E.)
Format: ENTER "filespec"
Example: ENTER "D:DEMOPR.INS"
This command causes the computer to move the file you
specify from the diskette into RAM. The program is entered in
untokenized form and is interpreted as the data is received. Enter,
unlike load, will not destroy a RAM-resident BASIC program, but
will merge the RAM-resident program and the disk file being
loaded. If there are duplicate line numbers in the two programs, the
line in the program being entered will replace the same line in the
RAM- resident program.
N0TE(N0.)
Format: NOTE #aexp , avar , avar
Example: 100 NOTE #1,X,Y
This command is used to store the current disk sector number
in the first arithmetic variable, (avar) and the current byte number
(within the sector) in the second avar. The numbers specify the
current read or write position and thus indicate where the next byte
to be read or written is located. The note command is used when
writing data to a disk file . The information in the note command is
written into a second file which is then used as an index into the first
file.
Note: aexp indicates an arithmetical expression. The item
placed here must have a numerical, not a string value.
P0INT(P.)
Format: POINT #aexp, avar, avar
Example: 100 POINT #2, A,B
This command is used when reading a file into RAM. The first
avar specifies the sector number and the second avar specifies the
128
byte within that sector where the next byte will be read or written.
Essentially, it moves a software-controlled pointer to the specified
location in the file. This gives the user "random" access to the data
stored on a disk file. The point and note commands are discussed in
more detail in your DOS Manual.
D0S(D0.)
Format: DOS
Example: DOS
The DOS command is used to go from BASIC to the disk
operating system (DOS) . If the disk operating system has not been
booted into memory, the computer will go into "Memo Pad" mode
and the user must press the system reset button to return to the
direct mode. If the disk operating system has been booted, the DOS
menu is displayed. To clear the DOS menu from the screen, press
the system reset button. Control then returns to BASIC. Control
can also be returned to BASIC by selecting B (Run Cartridge) on the
DOS menu.
DIRECTORY OF BASIC WORDS USED WITH DISK OPERATIONS
The following is an alphabetical director}' of BASIC reserved
words (words reserved for BASIC) used with disk operations . Note
that the period (.) is mandatory after all abbreviated keywords.
RESERVED
WORD:
ABBREVIATION
BRIEF SUMMARY
OF BASIC STATEMENT
CLOSE
CL.
I/O statement used to close a
disk file at the conclusion of
I/O operations.
DOS
DO.
This command causes the
menu to be displayed. The
menu contains all DOS utility
selections.
END
Stops program execution;
closes files; turns off sounds.
Program may be restarted
using cont.
ENTER
E.
I/O command used to retrieve
a listed program in unto-
129
kenized form . If a program or
lines are entered when a pro-
gram is resident in RAM,
enter will merge the two pro-
grams.
GET
GE.
Used with disk operation to
input a single byte of data into a
specified variable from a
specified device.
INPUT
This command requests data
from a specified device. The
default device is E: (Screen
Editor).
LIST
This command outputs the
untokenized version of a pro-
gram to a specified device.
LOAD
LO.
I/O command used to retrieve
a saved program in tokenized
form from a specified device .
OPEN
0.
Opens the specified file for
input or output operations.
PRINT
PR.or ?
I/O command causes output
from the computer to specified
output device.
PUT
PU.
Causes output of a single byte
of data from the computer to
the specified device.
SAVE
I/O statement used to record a
tokenized version of a program
in a specified file on a specified
device.
STATUS ST.
Calls status routine for a
specified device.
130
RESERVED ABBREVIATION BRIEF SUMMARY
Word: OF BASIC STATEMENT
TRAP T. Directs execution to a
specified line number in case
of an input error, allowing the
user to maintain control of
program.
XIO X. General I/O statement used in
a program to perform DOS
menu selections and specified
I/O commands.
BASIC ERROR MESSAGES USED DURING DISK OPERATION
The BASIC error messages used by the ATARI 810 disk
operating system are:
ERROR
CODE NO. ERROR CODE MESSAGE
2 Insufficient memory to store the statement or the new
variable name or to dim a new string variable.
3 Value Error: A value expected to be a positive integer
is negative; a value expected to be within a specific
range is not.
4 Too Many Variables: A maximum of 128 different
variable names is allowed.
5 String Length Error: Attempted to store beyond the
dimensioned string length.
6 Out of Data Error: Read statement requires more data
items than supplied by data statement(s) .
7 Number greater than 32767: Value is not a positive
integer or is greater than 32767.
8 Input Statement Error: Attempted to input a non-
numeric value into a numeric variable.
131
9 Array or String Dim Error: Dim size is greater than
32767 or an array/matrix reference is out of the range
of the dimensioned size , or the array /matrix or string
has already been dimensioned, or a reference has been
made to an undimensioned array or string.
10 Argument Stack Overflow: There are too many
gosubs or too large an expression.
11 Floating Point Overflow/Underflow Error: Attemp-
ted to divide by zero or refer to a number larger than
+1E98 or smaller than -1E99.
12 Line Not Found: A gosub, goto, or then referenced a
nonexistent line number.
13 No Matching For Statement: A next was encountered
without a previous for, or nested for/next statements
do not match properly. (Error is reported at the next
statement, not at for).
14 Line Too Long Error: The statement is too complex or
too long for BASIC to handle.
15 Gosub or For Line Deleted: A next or return state-
ment was encountered and the corresponding for or
gosub has been deleted since the last run.
16 Return Error: A return was encountered without a
matching gosub.
17 Garbage Error: Execution of "garbage" (bad RAM
bits) was attempted. This error code may indicate a
hardware problem, but may also be the result of faulty
use of poke. Try typing new or powering down, then
re-enter the program without any poke commands.
18 Invalid String Character: String does not start with a
valid character, or string in val statement is not a
numeric string.
19 Load Program Too Long: Insufficient memory re-
mains to complete load.
132
20 Device Number Larger than 7 or Equal to 0.
21 Load File Error: Attempted to load a nonload file.
The following are input/output errors that result during the
use of disk drives, printers, or other accessory devices.
128 Break Abort: User hit the break key during I/O oper-
ation.
129 Input/output Control Block (IOCB) already open:
Open statement within a program loop or IOCB al-
ready in use for another device or file.
130 Nonexistent Device Specified : Device is not turned on
or not attached.
131 IOCB Write Only: Command to a write-only device
(Printer).
132 Invalid Command: The command is invalid for this
device .
133 Device or File not Open: No open specified for the
device.
134 Bad IOCB Number: Illegal device number.
135 IOCB Read Only Error: Command to a read-only de-
vice.
136 EOF: End of File read has been reached. (NOTE:This
message can occur when using cassette files.)
137 Truncated Record: Attempt to read a record longer
than 256 characters.
138 Device Timeout. Device doesn't respond. Check con-
nections between peripheral equipment and console.
139 Device N AK : Garbage on serial port or bad disk drive .
140 Serial Bus input framing error.
133
141 Cursor Out of Range for particular mode .
142 Serial Bus Data Frame Overrrun.
143 Serial Bus Data Frame Checksum Error.
144 Device Done Error (invalid "done" byte) : Attempt to
write on a write-protected diskette.
145 Read After Write Compare Error (disk handler) or bad
screen mode handler.
146 Function not Implemented in handler.
147 Insufficient RAM for operating selected graphics
mode.
160 Drive Number Error.
161 Too Many Open Files (no sector buffer available) .
162 Disk Full (no free sectors).
163 Unrecoverable System Data I/O Error.
164 File Number Mismatch : Links on disk are messed up .
165 File Name Error.
166 Point Data Length Error.
167 File Locked.
168 Command Invalid (special operation code.)
169 Directory Full (64 files).
170 File Not Found.
171 Point Invalid.
134
Chapter 8
I/O Operations
This chapter describes input/output (I/O) devices and how data is
moved between them. The commands explained in this chapter are
those that allow access to the input/output devices. The input
commands are those associated with getting data into the RAM.
The output commands are those associated with retrieving data
from RAM.
As stated before, in order for the computer to be a useful
machine, it must be able to communicate with its user. The user
must be able to supply the computer with the programs and data
which enable it to perform some useful operation. In addition, the
computer must be able to provide an output showing the results of
the computations. The input/output section of the ATARI 800
provides this communications capability between the central pro-
cessing unit and the outside world.
The I/O section of the computer buffers (stores temporarily)
and controls data transfers between the computer memory and the
various peripheral devices. In the ATARI 800, the data transfers
take place in the central processing unit. They are under the control
of a computer program being executed by the CPU.
In small digital computers the I/O section is extremely simple ,
consisting generally of nothing more than some gating (devices that
output a signal when specified input conditions are met) and simple
control circuitry. In such computers, the data transfers take place
through the accumulator register. To read a word in from a
135
peripheral device , the computer executes an input instruction and
stores that word in the accumulator. Other instructions in the
program then cause that word to be stored in some specified mem-
ory location and/or used in a calculation.
Output operations are performed by first loading the ac-
cumulator with the desired word. An output instruction then causes
that word in the accumulator to be transferred to the peripheral
device. This basic form of I/O system is simple and desirable for
many types of computer operations. However, it is very slow and
inefficient.
The simplest form of input/output for any digital computer is a
system of binary switches and lights. A group of switches can act as
a temporary storage resister for a data word. The switches can be
set to their off or on positions corresponding to the binary ones and
zeros in the word to be used or entered. A button on the computer
can be used to store that word. At the same time, output can be
accomplished by placing lights on the various registers in the
machine. The lights will indicate the ones and zeros stored, for
example, in the accumulator register. The operator can read the
numbers stored there by interpreting the binary number rep-
resented by the lights. Binary switches and lights provide a low
cost, simple means of input/output operations in a computer. All
digital computers have this type of I/O capability.
Although binary lights and switches are widely used, they are
entirely inadequate for the bulk of most computer applications.
Consider the problem involved in storing, say, a 1000 word instruc-
tion program plus data in the computer's memory by using only a set
of input switches. The process would be extremely time-con-
suming, and the chances of making an error would be great. This
large program may produce a substantial number of output results
that the programmer wishes to observe. In such case, the pro-
grammer would have to observe the resulting words one at a time on
the binary lights of the accumulator register. This would be time-
consuming and inconvenient. As a result, more sophisticated
input/output methods are required.
Most of the I/O data in a digital computer is handled by
peripheral devices . Peripheral devices are machines that communi-
cate with the computer through the input/output section. You have
already seen several of these devices in Chapter 7. Peripheral
devices are, in effect, a man-made interface. These peripheral
devices not only speed up the input/output process tremendously,
136
but they also make it more convenient for the programmer and the
operator. Most peripheral devices use the decimal number system
and alphabet so that the operators and programmers do not have to
deal with binary numbers. In the ATARI 800, the input/output
keyboard simplifies the I/O process.
INPUT/OUTPUT DEVICES
The Central Input/Output (CIO) subsystem on the ATARI 800
provides the user with a single interface to access all of the system
peripheral devices in an independent manner. This means there is a
single entry point and a device-independent calling sequence. Each
device has a symbolic device name used to identify it; K, for
example, is used for keyboard. Each device must be opened before
it can be accessed, and each must be assigned to an I/O control
block. From then on, the device is referred to by its IOCB number.
ATARI BASIC contains 8 blocks in RAM which give the
operating system the information it needs to perform the I/O oper-
ation. This information includes the command, buffer length, buffer
address, and two auxiliary control variables. ATARI BASIC sets up
the IOCB's, but you must specify which IOCB to use. BASIC
reserves IOCB for I/O to the Screen Editor; therefore you may
not request ICOB 0. The graphics statement opens IOCB 6 for input
and output to the screen. IOCB 7 is used by BASIC for the LPRINT,
CLOAD, and CSAVE commands. The IOCB number may also be
referred to as the device number. IOCB's 1 through 5 are used in
opening the other devices for input/output operations. If IOCB 7 is
in use, it will prevent LPRINT or some of the other BASIC I/O
statements from being performed.
The ATARI 800 uses the following, I/O devices:
Keyboard. (K:) Input only device. The information you enter
is displayed on the screen as each key is pressed.
Line Printer: (P:) Output only device. The line printer prints
ASCII (American Standard Code for Information Interchange)
characters a line at a time. It recognizes no control characters.
Program Recorder: (C:) Input and Output device. The re-
corder is a read/write device which can be used as either one or the
other but never as both simultaneously. The cassette has two tracks
for sound and program recording purposes. The ATARI system
cannot put sound on the audio track but the sound on the track may
be played back through the TV speaker.
Disk Drives: (D1:,D2:,D3:,D4:) Input and Output devices. If
137
16K or RAM is installed, the ATARI can use from one to four disk
drives. If only one disk drive is attached, there is no need to add a
number after the device code D.
Screen Editor: (E:) Input and Output device. This device
uses the keyboard and the display to simulate a screen-editing
terminal . Writing to this device causes data to appear on the display
starting at the current cursor position. Reading from this device
activates the screen-editing process and allows the user to enter
and edit data. Whenever the return key is pressed, the entire logical
line within which the cursor resides is selected as the current
record to be transferred to the user program.
TV Monitor: (S:) Input and Output device. This device allows
the user to read characters from the display and write characters to
it using the cursor as the screen addressing mechanism. Both text
and graphics operations are supported.
Interface, RS-232: (R:) The RS-232 device enables the
ATARI system to interface with RS-232-compatible devices such as
printers, terminals, and plotters. It contains a port to which the
80-column printer (ATARI 825) can be attached.
INPUT AND OUTPUT COMMANDS
The following commands are used to control input from the
various peripherals and output to them. Because commands in-
volving disk operations have been described in Chapter 7, they will
not be covered again in this chapter.
General Commands Controlling I/O Devices
OPEN(0.)
CLOSE(CL.)
Formats : OPEN #aexp, aexpl,aexp2,filespec
CLOSE #aexpr
Examples: 100 OPEN #2,8,0,"D1:ATARI800.BAS"
100 A$="D1:ATARI800.BAS"
110 OPEN #2,8,0,A$
150 CLOSE #2
Before a device can be accessed, it must be opened. This
"opening" process links a specific IOCB to the appropriate device
handler, initializes any ClO-related control variables, and passes
any device-specific options to the device handler. The parameters
for the OPEN command are defined as follows:
138
Mandatory character that must be entered by the
user.
aexp
IOCB or file number. This number must be used
with the same parameters in future operations. It
may be any number from 1 through 7. It serves to
select the device that will be utilized.
aexpl
Code number to determine input or output opera-
tion.
Code 4 = input operation
8 = output operation
input and output operation
disk directory input operation
end-of-file append (output) opera-
12 =
6 =
9 =
tion.
Append is also used for a special screen editor
input mode. This mode allows a program to input
the next line from E: without waiting for the user
to press the return key.
aexp2
Device-dependent auxiliary code. An 83 in this
parameter indicates sideways printing on a
printer.
filespec Specific file designation. Must be enclosed in
quotation marks. The format for the file-spec
parameter is shown below.
Device —
Code
Device —
Number
(Optional)
"D 1 : V A T A R I 8 9 . B A S"
i>4
J
i
.File
Name
• Period
required
as separator
if extender
is used.
-Extender
Required Colon
The close command simply closes files that have previously
been opened with an open command. Note in the example that the
139
aexp number following the mandatory # character must be the same
as the aexp reference number in the open statement.
Other commands which are most often associated with a single
device, but which may be used to control other devices, are de-
scribed on the following pages under the topics "Controlling
Keyboard I/O" and "Controlling Output to the Screen"
Controlling Cassette Input and Output
CLOAD(CLOA.)
Format: CLOAD
Examples: CLOAD
100 CLOAD
This command can be used in either direct or deferred mode to
load a program from cassette tape into RAM for execution. After
you enter cload, one bell rings to indicate that you should press the
play button and then the return key. However, do not press the play
button until you have positioned the tape. Specific instructions for
cloading a program are contained in the ATARI 410 Program Recor-
der Manual. Steps for loading oversized programs are included in
the paragraphs under "Chaining Programs" at the end of this sec-
tion.
CSAVE(CS.)
Format: CSAVE
Examples: CSAVE
100 CSAVE
100 CS.
This command is usually used in Direct mode to save a RAM-
resident program onto cassette tape. Csave saves the tokenized
version of the program. When you enter csave two bells ring to
indicate that you should press the play and record buttons simul-
taneously and then press the return key. Do not, however, press
these buttons until the tape has been positioned. It is faster to save a
program using this command rather than a save "c" command
because short interrecord gaps are used.
Notes: Tapes saved using the two commands, save and csave, are
not compatible.
It may be necessary to enter an lprint before using csave.
Otherwise, csave may not work properly.
ENTER(E.)
140
Format: ENTER filespec
Examples: ENTER "C"
This statement causes a program originally recorded using the
list command to be loaded into RAM. The program is entered in
unprocessed (untokenized) form, and is interpreted as the data is
received. When the loading is complete, it may be run in the normal
way. The enter command may also be used with the disk drive as
outlined in Chapter 7. Note that both load and cload clear the old
program from memory before loading the new one. Enter merges
the old and new programs. This enter statement is usually used in
direct mode.
Controlling Keyboard I/O
INPUT(I.)
Format
™™ T H{:}]t v ^[{^}. . ]
Examples: 100 INPUT X
100 INPUT N$
100 PRINT "ENTER THE VALUE OF X"
100 INPUT X
This statement requests keyboard data from the user. The
computer displays a ? prompt when the program encounters an input
statement. The input statement is usually preceded by a print
statement that tells the user what type of information is being
requested. String variables are allowed only if they are not sub-
scripted. Matrix variables are not allowed.
The #aexp (arithmetic expression) is optional and is used to
specify the file or device number from which the data is to be input.
(See your owner's manual for the specifics.) If no #aexp is specified,
input is from the screen editor (E:). If several strings are to be input
from the screen editor, you must type one string, press the return
key, type the next string and press the return key again. Numerical
values can be typed on the same line separated by commas.
Controlling Output to the Printer
LPRINT(LP.)
Format: LPRINT exp , exp . . .
Example: LPRINT "PROGRAM TO CALCULATE X"
100 LPRINT X; " ";Y;" ";Z
141
This statement causes the computer to print data on the line
printer rather than on the screen. It can be used in either direct or
deferred modes . It requires no device specifier and no open or close
statement.
The following program listing illustrates a program that will
add 5 numbers entered by the user.
10 PRINT "ENTER 5 NUMBERS TO BE SUMMED"
20 FOR N=l TO 5
30 INPUT X
40 C=C+X
50 NEXT N
60 PRINT "THE SUM OF YOUR NUMBERS IS ";C
70 END
Controlling Output to the Screen
PRINT(PR or ?)
Format: PRINT #aexp , exp ,exp . . .
Examples: PRINT X,Y,Z,A$
100 PRINT' "THE VALUE OF X IS";X
100 PRINT "COMMAS", "CAUSE", "COLUMN",
"SPACING"
100 PRINT #3,A$
A print command can be used in either the direct or the
deferred mode . In the direct mode , this command prints whatever
information is contained between the quotation marks exactly as it
appears. In the first example, print X,Y,Z,A$, the screen will
display the current values of X,Y,Z,A$ as they appear in the RAM-
resident program. In the last example, print #3,A$, the 3 is the file
specifier (may be any number between 1 and 7) that specifies the
device where the value of A$ will be printed.
A comma causes tabbing to the next tab location. Several
commas in a row cause several tab jumps. A semicolon causes the
next expression or value to be placed immediately after the pre-
ceding expression with no spacing. Therefore, in the second exam-
ple, a space is placed before the ending quotation mark so the value
of X will not be placed immediately after the word "IS" . If no comma
or semicolon is used at the end of a print statement, a return is
output and the next print statement will start on the following line .
142
Chapter 9
Mathematical and Other Functions
The material in this chapter is designed to acquaint you with the
arithmetic, trigonometric, and special purpose functions incorpo-
rated in the ATARI BASIC system. A function performs a computa-
tion and returns the result which can be either printed or used in
additional computations. Included in the trigonometric functions are
two statements, radians (RAD) and degrees (DEG), that are fre-
quently used within trigonometric functions. Each function de-
scribed in this chapter may be used in either the direct or the
deferred mode. Multiple functions are perfectly legal.
The following functions and statements are described in this
section:
ABS
RND
COS
FRE
CLOG
SGN
SIN
PEEK
EXP
SQR
DEG/RAD
POKE
INT
ATN
ADR
USR
ARITHMETIC FUNCTIONS
ABS: This function returns the absolute value of a number
without regard to whether it is positive or negative. The returned
value is always positive.
CLOG: Returns the logarithm to the base 10 equivalent of the
143
variable or expression in parentheses. CLOG(O) should give an
error and CLOG(l) should be 0.
EXP: Returns the value of e raised to the power specified by
the expression in parentheses . In some cases , EXP is accurate only
to six significant digits.
INT: Returns the greatest integer less than or equal to the
value of the expression. This is true whether the value of the
expression is a positive or negative number. This INT function
should not be confused with the function used on calculators that
simply truncates (cuts off) all decimal places.
LOG: Returns the natural logarithm of the number or expres-
sion in parentheses. LOG(0) should give an error and LOG(l)
should be 0.
RND: Returns a hardware-generated random number between
and 1, but never returns 1. The variable or expression in paren-
theses following RND is a dummy and has no effect on the numbers
returned. However, the dummy variable must be used. Generally,
the RND function is used in combination with other BASIC state-
ments or functions to return a number for games, decision making,
and the like. Here's a simple routine that returns a random number
between and 999.
10 X=RND(0)
20 RX=INT(1000*X)
30 PRINT RX
SGN: Returns a - 1 if the value of an expression is a negative
number; a if it is 0, or a 1 if it is a positive number.
SQR: Returns the square root of an expression whose value is
positive.
TRIGONOMETRIC FUNCTIONS
ANT: Returns the arctangent of the variable or expression in
parentheses .
COS: Returns the trigonometric cosine of the expression in
parentheses .
SIN: Returns the trigonometric sine of the expression in
parentheses.
DEG/RAD: These two statements allow the programmer to
specify degrees or radians for trigonometric function computations.
The computer defaults to radians unless DEG is specified. Once the
DEG statement has been executed, RAD must be used to return to
radians.
144
SPECIAL PURPOSE FUNCTIONS
ADR: Returns the decimal memory address of the string
specified by the expression in parentheses . Knowing the address
enables the programmer to pass the information to USR routines ,
etc.
FRE: This function returns the number of bytes of user RAM
left. Its primary use is in the direct mode using a dummy variable (0)
to inform the programmer how much memory space remains for
completion of a program . Of course FRE can also be used with a
BASIC program in the deferred mode.
PEEK: Returns the contents of a specified memory address
location. The address specified must be an integer, or an arithmetic
expression that evaluates to an integer, between and 65535. It
must represent the memory address in decimal notation. The
number returned will also be a decimal integer with a range from
to 255. This function allows the user to examine either RAM or
ROM locations. In the first example below, the peek is used to
determine whether location 4000 (decimal) contains the number
255. In the second example below, the peek function is used to
examine the left margin.
Format: PEEK(aexp)
Examples: 1000 IF PEEK (4000) = 255 THEN PRINT 255
100 PRINT "LEFT MARGIN IS";PEEK (82)
POKE: Although this is not a function, it is included in this
chapter because it is closely associated with the peek function. The
poke command inserts data into the memory location or modifies
data already stored there. Note that the data must be a decimal
number between and 255. Poke cannot be used to alter ROM
locations. While you are gaining familiarity with this command, you
should look at the memory location using a peek and write down the
contents of the location. Then, if the poke doesn't work as antici-
pated, the original contents can be poked back into the location.
USR: This function returns the results of a machine-language
subroutine. The first expression (aexpl) must be an integer, or an
arithmetic expression whose value is an integer, that represents
the decimal memory address of the machine language routine to be
performed. Subsequent input arguments, aexp2, aexp3, etc., are
optional . These should be arithmetic expressions within a decimal
range of through 65535. If a noninteger value is used it will be
rounded off to the nearest integer.
145
N (Number of arguments on the stack-may be 0)
X , (High byte of argument X)
X 2 (Low byte of argument X)
Y , (High byte of argument Y)
Y 2 (Low byte of argument Y)
Z , (High byte of argument Z)
Z 2 (Low byte of argument Z)
R, (Low byte of return address)
R 2 (High byte of return address)
Fig. 9-1. Hardware stack definition.
These values returned will be converted from BASIC'S Binary
Coded Decimal floating point number format to a two-byte binary
number; then pushed onto the hardware stack. The hardware stack
is composed of a group of RAM locations under the direct control of
the 6502 microprocessor chip. Figure 9-1 illustrates the structure of
the hardware stack.
146
Chapter 10
Programming
Techniques to Save Memory
This chapter includes hints on increasing programming efficiency
and conserving memory. These hints give ways of conserving
memory on the ATARI 800. Some of these methods make programs
less readable and harder to modify, but there are cases when this is
necessary due to memory limitations.
1. In many small computers, eliminating blank spaces be-
tween words and characters as they are typed into the
keyboard will save memory. This is not true of the ATARI
800, which automatically removes extra spaces. Statements
are always displayed in the same manner no matter how many
spaces were used on program entry. Spaces should be used
(just as in typing on a conventional typewriter) between suc-
cessive words and between words and variable names . Here
is an example:
10 IF A = 5 THEN PRINT A
Note the space between IF and A and between then and print.
In most cases, a statement will be interpreted correctly by the
computer even if all spaces are left out, but this is not always true.
Therefore use conventional spacing.
2. Each new line number represents the beginning of what is
called a new "logical line". Each logical line takes 6 bytes of
"overhead", whether it is used to full capacity or not. Adding
147
an additional BASIC statement by using a colon (:) to separate
each pair of statements on the same line takes only 3 bytes . If
you need to save memory, avoid programs like the following:
10 X=Y+1
20 Y=Y+1
30 Z=X+Y
40 PRINT Z
50 GOTO 50
and consolidate lines like this:
10 X=X+1:Y=Y+1:Z=X+Y:PRINTZ: GOTO 10
The above consolidation saves 12 bytes.
3. Variables and constants should be "managed" for savings,
too. Each time a constant (4,5,16,3.14, etc.) is used, it takes 7
bytes. Defining a new variable requires 8 bytes plus the
length of the variable name (in characters) . But each time it is
used after being defined, it takes only 1 byte , regardless of its
length . Thus , if a constant is used more than once or twice in a
program, it should be defined as a variable, and the variable
name should be used throughout the program. For example:
10 PI=3.14159
20 PRINT "AREA OF A CIRCLE IS THE RADIUS
SQUARED TIMES ";PI
4. Literal strings found in print statements require 2 bytes
overhead and 1 byte for each character (including all spaces) in
string.
5. String variables take 9 bytes each, plus the length of the
variable name (including spaces), plus the space eaten up by
the DIM statement , plus the size of the string itself when it is
defined. Obviously, the use of string variables is very costly
in terms of RAM.
6. Definition of a new matrix requires 15 bytes, plus the
length of the matrix variable name, plus the space needed for
the DIM statement, plus 6 times the size of the matrix. Thus,
a 25 row by 4 column matrix would require 15 + (approxi-
mately) 3 -I- (approximately) 10+6 times 100, or about 630
bytes .
148
Chapter 1 1
Sample Programs: Conversions
In this day and age conversions are quite common . . . Celsius to
Fahrenheit, centimeters to inches, dollars to pesos . . .just to name
a few. The ATARI can be used to help you make these conversions
quickly and easily. The following programs are examples of several
such conversions. Other uses for the programs should readily come
to mind as you read through these .
CURRENCY EXCHANGE
More and more Americans are traveling to foreign countries
each year, and as you know, monetary values are different. Let's
assume that you plan a trip to Britain and France and you wish to
convert monetary values among three systems: British pound,
French franc, and U.S. dollar. In order to facilitate these conver-
sions, you decide to write a program to compute them for you. Each
currency system is to be denoted by a code number. You must
initialize the program each time you use it by entering equivalent
monetary values for each currency . Then you can enter the currency
code and the amount to be converted. The currency system and the
equivalent amount will be printed.
On a certain morning, 1 British pound is equivalent to 8.3981
francs and 1.8248 U.S. dollars. At these rates, find how much an
airplane ticket worth 284 British pounds will cost in dollars and in
francs. Do the same for an English double-barreled shotgun valued
at 1205 U.S. dollars.
149
10
REM* CURRENCY EXCHANGE
20
PRINT "ENTER CODE, AMT FOR 3
SYSTEMS"
30
PRINT "1=BR, 2=FR, 3=US"
40
INPUT C1,A1,C2,A2,C3,A3
50
PRINT
60
PRINT "CODE, AMT TO CONVERT (
0,0=STOP)"
70
INPUT C,A
80
IF C=0 THEN STOP
90
REM * DETERMINE REFERENCE
100
ON C GOTO 110,130,150
110
R=A1
120
GOTO 160
130
R=A2
140
GOTO 160
150
R=A3
160
V1=A*A1/R
170
V2=A*A2/R
180
V3=A*A3/R
190
PRINT "EQUIVALENT AMOUNTS:"
200
PRINT "BR. POUND ";V1
210
PRINT "R.F. FRANC ";V2
220
PRINT "U.S. DOLLAR ";V3
230
PRINT
240
GOTO 50
250
END
Display
When the following is run, you will see the following on your
screen:
ENTER CODE, AMT FOR 3 SYSTEMS
1=BR, 2=FR, 3=US
1:1,2,8.3981,3,1.8248
CODE, AMT TO CONVERT (0,0=STOP)
1,284
EQUIVALENT AMOUNTS
BR. POUND 284
R.F. FRANC 2385
150
U.S. DOLLAR 518
CODE, AMT TO CONVERT (0,0=STOP)
?
3,1205
EQUIVALENT AMOUNTS
BR. POUND 669
R.F. FRANC 5622
U.S. DOLLAR 1205
CODE, AMT TO CONVERT (0,0=STOP)
?
0,0
METRIC CONVERSIONS
The metric system will eventually become universal— or so it
seems at this time— and the ATARI can be programmed to make
these conversions for you. The program which follows allows con-
versions of length, area, mass (weight), and liquid volume. The
conversion can be either to or from the metric units .
10
REM* METRIC CONVERSION PROGRAM
20
M=8
30
Ml=9
40
M2=6
50
M3=8
60
DIM Ll$(8)
70
DIM L2$(8)
80
DIM L3(8)
90
DIM Al$(9)
100
DIM A2$(9)
110
DIM A3(9)
120
DIM Wl$(6)
130
DIM W2$(6)
140
DIM W3(6)
150
DIM Vl$(8)
160
DIM V2$(8)
170
DIM V3(8)
180
FOR I = 1 TO M
190
READ LI$(I),L2$(I),L3(I)
200
NEXT I
210
FOR I = 1 TO Ml
220
READ A1$(I),A2$(I),A3(I)
230
NEXT I
151
240 FOR I = 1 TO M2
250 READ W1$(I),W2$(I),W3(D
260 NEXT I
270 FOR I = 1 TO M3
280 READ VI$(I),V2$(I),V3(I)
290 NEXT I
300 REM *********
310 REM **** PROCESSING AREA *****
320 PRINT'DO YOU WISH TO CONVERT LENGTH (L),
AREA (A),"
330 PRINT" MASS (M), OR LIQUID VOLUME (V)?"
340 INPUT Al$
350 PRINT
360 PRINT: CONVERSIONS AVAILABLE"
370 PRINT
380 PRINTTAB(9);"NER";TAB(14);"
FROM";TAB(39);" TO"
390 PRINTTABO);"— ";TAB(14);" ";TAB(39);"
400 IF A1$="L" THEN 460
410 IF A1$="A" THEN 590
420 IF A1$="M" THEN 720
430 IF A1$="V" THEN 850
440 PRINT'ENTRY MUST BE L, A, M, OR V"
450 GOTO 300
460 REM **** PRINT FOR LENGTH ****
470 FOR I = 1 TO M
480 PRINTAB(10);I;TAB(15);L1$(I);TAB(40);L2$(I)
490 NEXT I
500 PRINT
510 PRINT'ENTER THE NUMBER OF THE CONVERSION
TO BE USED (0 WHEN DONE)";
520 INPUT N
530 IF N=0 THEN 980
540 PRINT'ENTER THE NUMBER OF ";L1$(N)
550 INPUT L0
560 L=L0*L3(N)
570 PRINTL0;L1$(N);"="L;L2$(N)
580 GOTO 500
590 REM **** PRINT OF AREA ****
600 FOR I = 1 TO Ml
610 PRINTTAB(9);I;TAB(14);A1$(I);TAB(39);A2$(I)
620 NEXT I
152
630 PRINT
640 PRINT'ENTER THE NUMBER OF THE CONVERSION
TO BE USED (0 WHEN DONE)"
650 INPUT N
660 IF N=0 THEN 990
670 PRINT'ENTER THE NUMBER OF ";A1$(N);
680 INPUT A0
690 A=A0*A3(N)
700 PRINT A0;A1$(N);"=";A;A2$(N)
710 GOTO 630
720 REM ******** PRINT OF MASS *********
730 FOR I = 1 TO M2
740 PRINTTAB(10);I;TAB(15);W1$(I);TAB(40);W2$(I)
750 NEXT I
760 PRINT
770 PRINT'ENTER THE NUMBER OF THE CONVERSION
TO BE USED (0 WHEN DONE)";
780 INPUT N
790 IF N=0 THEN 990
880 PRINT'ENTER THE NUMBER OF ";W1$(N);
810 INPUT W0
820 W=W0*W3(N)
830 PRINTW0/W1$(N); "=";W;W2$(N)
840 GOTO 760
850 REM **** PRINT OF LIQUID VOLUME ****
860 FOR I = 1 TO M3
870 PRINTTABC1 0) ; I ;TAB(15) ; V1$(I) ;TAB(40) ; V2$(I)
880 NEXT I
890 PRINT
900 PRINT'ENTER THE NUMBER OF THE CONVERSION
TO BE USED (0 WHEN DONE)";
910 INPUT N
920 IF N=0 THEN 990
930 PRINT'ENTER THE NUMBER OF ";V1$(N);
940 INPUT V0
950 V=V0*V3(N)
960 PRINTV0;V1$(N);"=";V;V2$(N)
970 GOTO 890
980 REM *********
990 REM ****** PROGRAM TERMINATION POINT ******
1000 PRINT
1010 PRINT "END"
153
1020 END
1030 REM **********
1040 REM ***** DATA FOR INITIALIZATION *******
1050 REM ****** LENGTH *****
1060 DATA INCHES, MILLIMETERS, 25.4, FEET, ME-
TERS,. 3048
1070 DATA YARDS, METERS, .0144, MILES, KILOME-
TERS, 1.6093
1080 DATA MILLIMETERS, INCHES,.0394,METERS,FEET,
3.2808
1090 DATA METERS, YARDS, 1.0936, KILOMETERS,
MILES, .6214
1100 REM ******* AREA
1110 DATA SQ INCHES, SQ CENTIMETERS,6.4516,SQ
FEET,SQ METERS,. 0929
1120 DATA SQ YARDS.SQ METERS,. 8361 ,SQ MILES,SQ
KILOMETERS ,2.59
1130 DATA ACRES ,SQ HECTOMETERS(HECTARES),.4047
1140 DATA SQ CENTIMETERS.SQ INCHES, .115.SQ MET-
ERS,SQ YARDS.1.196
1150 DATA SQ KILOMETERS, SQ MILES,. 3861
1160 DATA SQ HECTOMETERS(HECTARES), ACRES, 2.471
1170 REM **** MASS
1180 DATA OUNCES, GRAMS, 28. 3495, POUNDS, KILO-
GRAMS,. 4536
1190 DATA SHORT TONS, MEGAGRAMS,.9,GRAMS,
OUNCES,. 0353
2000 DATA KILOGRAMS ,POUNDS,2.2046,MEGAGRAMS
, SHORT TONS, 1.1
1200 REM ******* LIQUID VOLUME
1220 DATA OUNCE, MILLILITERS ,30, PINTS .LITERS,. 4732
1230 DATA QUARTS, LITERS,. 9464, GALLONS, LITERS,
3.7856
1240 DATA MILLILITERS,OUNCES,.03,LITERS,PINTS,
2.1134
1250 DATA LITERS,QUARTS,1.0567,LITERS, GALLONS,
.2642
1260 REM *********
Display: When the program is run, you may see the following
on your screen:
154
DO YOU WISH TO CONVERT LENGTH (L), AREA (A),
MASS (M), OR LIQUID
VOLUME (V)?
?L
CONVERSIONS AVAILABLE
NBR
FROM
INCHES
TO
1
MILLIMETERS
2
FEET
METERS
3
YARDS
METERS
4
MILES
KILOMETERS
5
MILLIMETERS
INCHES
6
METERS
FEET
7
METERS
YARDS
8
KILOMETERS
MILES
ENTER THE NUMBER OF THE CONVERSION TO BE USED (0
WHEN DONE)? 3
ENTER THE NUMBER OF YARDS? 10
10 YARDS= 9.144 METERS
ENTER THE NUMBER OF THE CONVERSION TO BE USED (0
WHEN DONE)?
END
If you run the program again and do a different conversion, you
may see the following:
DO YOU WISH TO CONVERT LENGTH (L), AREA(A),
MASS (M), OR LIQUID VOL-
UME (V)?
?A
CONVERSIONS AVAILABLE
NBR FROM
TO
1 SQ INCHES
2 SQ FEET
3 SQ YARDS
4 SQ MILES
5 ACRES
6 SQ CENTIMETERS
7 SQ METERS
8 SQ KILOMETERS
9 SQ HECTOMETERS(HECTARES)
SQ CENTIMETERS
SQ METERS
SQ METERS
SQ KILOMETERS
SQ HECTOMETERS
(HECTARES)
SQ INCHES
SQ YARDS
SQ MILES
ACRES
155
ENTER THE NUMBER OF THE CONVERSION TO BE USED (0
WHEN DONE)? 4
ENTER THE NUMBER OF SQUMILES? 10
10 SQ MILES=25.9 SQ KILOMETERS
ENTER THE NUMBER OF THE CONVERSION TO BE USED (0
WHEN DONE)?
END
156
Chapter 12
More Programs
The following programs in BASIC can be run as they are for experi-
ence and then modified to suit your own personal needs. For
example, the one on gun collecting could be modified to be used to
organize a coin collection ... or perhaps your bottle or old canning
jar collection.
To give you some experience with you ATARI 800, some of the
programs will require a slight modification to make them work. Can
you make them work?
FINDING GREATEST COMMON DIVISOR OF TWO NUMBERS
Description
This program finds the greatest common divisor of two num-
bers.
Functions of the Program
The program reads in the number of greatest common divisors
to be found and then the pairs of numbers for which the greatest
common divisors are desired. You, however will have to supply the
lines that will determine the greatest common divisor.
Instruction for Use
Use data statements to supply the number of pairs of numbers
for which a G.C.D. is desired, followed by those pairs of numbers.
157
Data Format
The format to put the data in is:
1. Number of greatest common divisors needed.
2. First number of first pair.
3. Second number of first pair.
4. First number of second pair, etc.
Output Description
Appropriate headings with columns of supplied data and the
calculated G.C.D. (if you add the right lines).
10 REM This program finds the greatest common divisor of 2
numbers
15 REM N is the number of pairs of numbers
20 REM A and B are the two numbers for which a G.C.D. is
desired
25 REM Q is the quotient and R is the remainder of A/B
30 READ N
35 PRINT "NUMBER OF G.C.D. to be found is ",N
37 PRINT
40 IFN=0THEN99
45 PRINT"A","B","GCD"
50 READA.B
55 PRINT A,B;
60 LET Q = INT (A/B)
65 LETR=A-Q*B
70 IFR=0THEN90
75 LETA=B
80 PRINT B
85 GOTO 60
90 PRINT B
92 LETN=N-1
94 IFN=0THEN99
95 GOTO 50
97 DATA 3,256,243,5,15,130.169
99 END
RUN
Number of G.C.D. s to be found is 3
A B G.C.D.
256 243 1
158
5 15 5
130 169 13
PROGRAM FOR GUN COLLECTORS
Description
This program enables gun collectors to organize and control
their collections. All the items in your collection can be listed, or
you can select items by the manufacturer.
Functions of the Program
The program accepts the gun information from the data state-
ments and prints the items specified. Items to be printed can be
selected according to manufacturer or the entire list can be printed.
Watch out! Some of the program lines will have to be fixed. A few
hints : Are the same variable names used for different variables ? Are
variable names changed or confused? Are string variables used
where necessary? Are there references to nonexistent line num-
bers?
Instructions for Use
Use data statements to enter the total number of guns to be
listed and to enter the pertinent information concerning each gun.
Data Format
The format to put the data in is: manufacturer, model number,
serial number, type of action, caliber or gauge, condition, value.
Output Description
See the example below. Output is either a formatted list of all
items or a list of those items that satisfy the selection criteria.
Important Variables
M ..Maximum number of data reads
(total number of guns to be entered)
M2 ..Manufacturer of gun
N ..Model number
S ..Serial number
C . .Caliber or gauge
A . -Type of action
C2 . .Condition
V . .Current Value
159
10 REM GUN COLLECTION PROGRAM
20 REM*** READ DATA***
30 PRINT "ENTER TOTAL NUMBER OF GUNS TO BE
RECORDED"
40 INPUT M
50 PRINT "DO YOU WISH TO HAVE ALL ENTRIES
LISTED? (Y OR N)"
60 INPUT L$
70 PRINT
80 IF L$ = "Y" THEN 110
90 PRINT "ENTER MANUFACTURER YOU WISH LISTED"
100 INPUT L0
110 PRINT
120 PRINT
130 PRINT "MANUFACTURER", TAB(IS); "Model"
TAB(10); "Serial";
140 PRINT TAB(10); "Caliber" ;TAB(10); "Action";TAB(10);
150 PRINT "Condition"; TAB(10); "Value"
155 PRINT
160 FOR 1=1 TO M
170 READ 11$
180 IF 11$ = "END" THEN 320
190 READ M2,N,S,C,A,C2,V
200 IF Z$ <> "Y" THEN 240
210 PRINT 11$; TAB(10); A; TAB(IS); C2; TAB(r);V
230 GOTO
240 IF 11$ <> A0 THEN 310
250 C=C+1
260 IF C=l THEN 290
270 11$=" "
280 PRINT 11$; TAB (IS);M2; TAB(10);S:TAB(10);
300 PRINT C; TAB(10); A; TAB(IS);C2; TAB(S);V
310 NEXT I
320 PRINT
330 PRINT
340 STOP
350 REM*** DATA***
360 DATA Winchester, 70, 44271, .270W,Bolt,Good, 450
370 DATA Remington, 1100, 00714, 12, Auto, Ex, 312
380 DATA H and R, 158C, 77431, 20, single, good, 95
390 DATA Remington, 742, 00853, .30-06, auto, ex, 375
400 DATA END
160
RUN
ENTER TOTAL NUMBER OF GUNS TO BE RECORDED ?4
DO YOU WISH TO HAVE ALL ENTRIES LISTED? (Y OR N) ? Y
Manufacturer Model Serial Caliber Action Condition Value
Winchester
70
44371
.270W
Bolt
Good
450
Remington
1100
00714
12
Auto
Ex
312
HandR
158C
77431
20
Single
Good
95
Remington
742
00853
30-06
Auto
Ex
375
RUN
ENTER MAXIMUM NUMBER OF GUNS TO BE RECORDED
?4
DO YOU WISH TO HAVE ALL ENTRIES LISTED? (Y OR N) N
?Remington
Manufacturer Model Serial Caliber Action Condition Value
Remington 1100 00714 12 Auto Ex 312
742 00853 30-06 Auto Ex 375
CHECKBOOK BALANCER
This is one of the "traditional" programs that every beginning
computerist writes. It allows the entry of outstanding checks and
uncredited deposits as well as cleared checks and credited deposits .
Remember that the question mark is simply a symbol for print.
10 DIM A$(30),MSG$(40),MSG1$(30),MSG2$(30)
,MSG3$(30) ,MSG4$(30) ,MSG5$(30) ,MSG6$(30)
20 OUTSTAND=0
30 GRAPHICS 0:? :? " CHECKBOOK BALANCER":?
40 ? "You may make corrections at any time by entering a
negative dollar value."
50 MSGl$="OLD CHECK - STILL OUTSTANDING"
60 MSG2$="OLD DEPOSIT -- NOT CREDITED"
70 MSG3$= "OLD CHECK - JUST CLEARED"
80 MSG4$= "OLD DEPOSIT - JUST CREDITED"
90 MSG5$= "NEW CHECK (OR SERVICE CHARGE)"
100 MSG6$="NEW DEPOSIT (OR INTEREST)"
150 TRAP 150:? "Enter beginning balance from your
checkbook";: INPUT YOURBAL
160 TRAP 160:? "Enter beginning balance from your
bankstatement";:INPUT BANKBAL
165 TRAP 40000
170 GOTO 190
180 CLOSE #1:? "PRINTER IS NOT OPERATIONAL."
161
185 ? "PLEASE CHECK CONNECTORS."
190 PERM=0
200 ? "Would you like a permanent record on the printer" ;:IN-
PUTA$
210 IF LEN(A$)=0 THEN 200
220 IF A$(1,1)="N" THEN 400
230 IFA$(1,1)"Y"THEN200
240 TRAP 180
250 LPRINT :REM TEST PRINTER
260 PERM=1
280 LPRINT "YOUR BEGINNING BALANCE IS $";YOUR-
BAL
290 LPRINT "BANK STATEMENT BEGINNING BALANCE
IS $";BANKBAL; LPRINT
400 TRAP 400: ?: ? "Choose one of the following:"
410 ? "(1) ";MSG1$
415 ? "(2) ";MSG2$
420 ? "(3) ";MSG3$
425 ? "(4) ";MSG4$
430 ? "(5) ";MSG5$
435 ? "(6) ";MSG6$
440 ? "(7) ";NO MORE ENTRIES"
490 ?
500 INPUT N:IFN<1 OR N>7 THEN 400
505 TRAP 40000
510 ON N GOSUB 1000,2000,3000,4000,5000,6000,7000
520 MSG$="NEW CHECKBOOK BALANCE IS": AMOUNT
=YOURBAL: GOSUB 8000
530 MSG$="NEW BANK STATEMENT BALANCE
IS":AMOUNT=BANKBAL:GOSUB 8000
540 MSG$ ="OUTSTANDING CHECKS- DEPOSITS="
:AMOUNT=OUTSTAND:GOSUB 8000
545 IF PERM THEN LPRINT
550 GOTO 400
1000 REM OLD CHECK - STILL OUTSTANDING
1010 MSG$=MSGl$:GOSUB 8100
1020 OUTSTAND=OUTSTAND+AMOUNT
1030 RETURN
2000 REM OLD DEPOSIT - STILL NOT CREDITED
2010 MSG$=MSG2$:GOSUB 8100
2020 OUTSTAND=OUTSTAND- AMOUNT
162
2030 RETURN
3000 REM OLD CHECK - - JUST CLEARED
3010 MSG$=MSG3$:GOSUB 8100
3020 BANKBAL=BANKBAL- AMOUNT
3030 RETURN
4000 REM OLD DEPOSIT - JUST CREDITED
4010 MSG$=MSG4$:GOSUB 8100
4020 BANKBAL=BANKBAL+AMOUNT
4030 RETURN
5000 REM NEW CHECK (OR SERVICE CHARGE) - JUST
CLEARED
5010 MSGS=MSG5$:GOSUB 8100
5020 YOURBAL=YOURBAL- AMOUNT
5030 ? "IS NEW CHECK STILL OUTSTANDING"; :INPUT A$
5040 IF LEN(A$)=0 THEN 5030
5050 IF A$(l,l) "N" THEN 5060
5055 BANKBAL=BANKBAL- AMOUNT
5057 IF PERM THEN LPRINT "CHECK HAS CLEARED."
5058 RETURN
5060 IF A$(l,l)o"Y" THEN 5030
5070 OUTSTAND=OUTSTAND+AMOUNT
5075 IF PERM THEN LPRINT "CHECK IS STILL OUT-
STANDING."
5080 RETURN
6000 REM NEW DEPOSIT (OR INTEREST) - JUST CRE-
DITED
6010 MSG$=MSG6$:GOSUB 8100
6020 YOURBAL=YOURBAL+AMOUNT
6030 ? "HAS YOUR NEW DEPOSIT BEEN CREDITED" -IN-
PUT A$
6040 IF LEN(A$)=0 THEN 6030
6050 IF A$(l,l)< >"Y" THEN 6060
6052 BANKBAL=BANKBAL+AMOUNT
6053 IF PERM THEN LPRINT" DEPOSIT HAS BEEN CRE-
DITED."
6055 RETURN
6060 IF A$(l,l)< >"N" THEN 6030
6070 OUTSTAND=OUTSTAND- AMOUNT
6075 IF PERM THEN LPRINT "DEPOSIT HAS NOT BEEN
CREDITED."
6080 RETURN
163
7000 REM DONE
7010 ? "BANK'S BALANCE MINUS (OUTSTAND-
ING CHECKS- DEPOSITS) SHOULD NOW EQUAL
YOUR CHECKBOOK BALANCE."
7020 DIF=YOURBAL- (BANKBAL- OUTSTAND)
7030 IF DIF< >0 THEN 7040
7035 ? "IS $";BANKBAL;" THE ENDING BALANCE ON YOUR
BANK STATEMENT" ;:INPUT A$
7036 IF LEN(A$)=0 THEN 7035
7037 IF A$(1,1)="Y" THEN ? CONGRATULATIONS: YOUR
CHECKBOOK BALANCES!" :END
7038 GOTO 7060
7040 IF DIF>0 THEN ? "YOUR CHECKBOOK TOTAL IS
$";DIF;" OVER YOUR BANK'S TOTAL. ":GOTO 7060
7050 ? "WOULD YOU LIKE TO MAKE CORRECTIONS?"
7070 ? "REMEMBER, YOU CAN ENTER A NEGATIVE DOL-
LAR VALUE TO MAKE A CORRECTION.
7080 ? "ENTER Y OR N";:INPUT A$
7090 IF LEN(A$)=0 THEN END
7100 IF A$(1,1)="Y" THEN RETURN
7110 END
7999 REM MSG PRINTING ROUTINE
8000 ? MSG$;" $";AMOUNT
8010 IF PERM=1 THEN LPRINT MSG$;" $";AMOUNT
8020 RETURN
8100 REM MSG PRINT & INPUT ROUTINE
8110 TRAP 8110:? "ENTER AMOUNT FOR ";MSG$;:INPUT
AMOUNT
8120 TRAP 40000
8130 IF PERM=1 THEN LPRINT MSG$;" $";AMOUNT
164
Chapter 13
Flowcharting Techniques
If you are a beginning programmer, you may be interested in
learning some of the techniques that allow you to more easily
advance a programming task from a conceptual stage to a finalized
stage.
Flowcharts, which pictorialize the solution to a programming
task, are valuable programming tools. They are often drawn long
before the actual program statements are written.
While flowcharting your program, you might change or
simplify your approach, or see a flaw in your logic. After several
attempts, you should have a workable flowchart and, once you do,
your programming task is greatly reduced.
Any flowchart that you draw is useful; but a few basic conven-
tions are described in this chapter. Terminal (that is, starting or
ending) activities are represented by ovals. Arrows, indicate the
direction of program flow between operations. Most calculator
operations are represented by rectangles . A diamond represents a
decision point.
To illustrate, in the following example we have labeled each
flowcharting operation with the corresponding program line
number. See Fig. 13-1. As you can see, once the flowchart is
finalized, the program can be written relatively easily.
10 REM-THIS PROGRAM AVERAGES UP TO 20 POSI-
TIVE NUMBERS
20 REM-IF YOU HAVE FEWER THAN 20 NUMBERS TO
165
Line Number
40
50
60
70
80
90
110
120
130
f START J
INITIALIZE
TOTALING
VARIABLE
START LOOP
WITH
COUNT VARIABLE!
= <20
TOTAL = TOTAL
&
NUMBER
(3d
fr>20
l = l- 1 I*
PRINT
\A/\
f END j
Fig. 13-1.
166
ENTER.
30 REM-ENTER A NEGATIVE NUMBER TO END THE
INPUTTING.
40 A=0
50 FOR 1=1 TO 20
60 INPUT B
70 IF B <0 THEN 110
80 A=A+B
90 NEXT I
110 1=1-1
120 PRINT "THE AVERAGE OF THE "I" NUMBERS IS "A/I
130 END
As mentioned previously, flowcharts use boxes and lines,
following a few simple rules , to represent a program design . Only a
few shapes and a few ways of drawing the connecting lines are used .
These restrictions are intended to make the resulting flowcharts
easy to understand by displaying the relationship of parts very
clearly . After a correct flowchart has been drawn , translation to a
program (writing statements corresponding to the boxes) is rela-
tively simple.
FLOWCHARTING SYMBOLS
Five different shapes of boxes are required for most flow-
charts .
Rectangle
A rectangle indicates any processing operation except input/
output or a decision.
Diamond
A diamond indicates a decision. The lines leaving the box are
labeled with the results that cause each path to be followed.
Parallelogram
A parallelogram indicates an input or output operation.
Oval
An oval indicates the beginning or ending point of a program or
program segment.
167
Circle
A small circle indicates a collection point, where lines from
other boxes join.
CONTROL STRUCTURES
The fundamental function of a flowchart, as of any other pro-
gram design tool , is to show in exact and unambiguous detail the
sequence in which actions are to be carried out and the conditions
under which alternatives are to be taken . In depicting these matters
in flowcharts, three control structures are normally used.
Sequence
When an arrow leads from one box to the next, that means
simply that the two are to be executed in sequence in the order
shown.
Selection
The choice indicated by the decision box always has just two
outcomes, depending on whether the condition is true or false.
Iteration
Processing actions are executed repeatedly until a stated con-
dition terminates the repetition. The number of repeats may in
some cases be zero.
The basic structures stated above may be combined. For exam-
ple , a path coming out of a decision box may lead to another decision
or perhaps an iteration. Furthermore, it will commonly happen that
the actions specified in a loop will include decisions. This is per-
fectly acceptable so long as only the three basic structures are used.
THE IF STATEMENT
Often there are times when you want to make a decision. In the
averaging program discussed previously, we wanted the program to
branch to either the end of the program, or to the inquiry for more
information. The branch was dependent on the outcome of a
specified condition, using the if . . . then statement.
IF numeric expression THEN statement
The if . . . then statement makes a decision based upon the
outcome of the numeric expression. If the expression is true, the
then part of the statement is executed. If the outcome is false,
168
execution continues with the statement following the if . . . then
statement.
For example , suppose an accountant wishes to write a program
that will calculate and print the amount of tax to be paid by a number
of persons. For those with incomes of $10, 000 per year or less, the
amount of tax is 17.5%. For those with incomes of over $10,000, the
tax is 20%. A flowchart for the program might look like the one in
Fig. 13-2. The diamond in the flowchart would be represented by an
if . . . then statement in a program. The program may look like the
following:
10 PRINT "INCOME"
20 INPUT I
30 IF I > 10000 THEN 60
40 PRINT"TAX=";I*.175
50 GOTO 70
60 PRINT"TAX=";I*.2
70 END
As you can see, we used a relational operation in the if . . . then
statement. The if . . . then statement is most often used with
relational operators, although the decision can be based on the value
of any numeric expression.
If the condition is true— the income is greater than $10,000—
program control is transferred to statement 60. If the condition is
false— the income is less than or equal to $10,000— the rest of the if
statement is ignored and the program continues at statement 40. To
test this program, use the values of $20,000 and $9,000.
THE ELSE OPTION
The ATARI does not have the else option, however its action
is useful to study while discussing flowcharts. In the previous
example , if the numeric expression was evaluated as false , program
execution continued with the next sequential statement following
the if . . . then statement. But if you specify the else option with the
if . . . then statement, the program will instead perform the instruc-
tions that follow the else. This gives you tremendous power using
conditional branching.
IF numeric expression THEN state number or executable instr.
ELSE statement number or executable instr.
If the numeric expression is false and else is specified execu-
tion is transferred to the statement number following else or the
169
Line Number
10
f START J
*
20
PRINT
PROMPT
30
/
/ INPUT
INCOME /
7
YES
40
^INCOME >S
\ 10,000 /
Yno
50
L
/ OUTPUT
INCOME • j
.175 /
/
*
GOTO
END
60
/
/ OUTPUT
' INCOME *
/U
Y
70
f END J
Fig. 13-2.
170
indicated else statement is executed. Look at the following exam-
ple.
A quadratic equation is of the form 0=ax 2 +bx+c. If a=0, its
two roots may be found by the formulas
-b+Vb 2 - 4 ac -b-Vb 2 - 4 ac
r ' = S andr2 = &
To write a program to compute the roots of a quadratic equa-
tion given the values of the coefficients a, b, and c, proceed as
follows: If a is zero, display an error message and reenter new
values. If b 2 - 4 ac is less than zero, then the square root of that
value would give a warning message or an error. So make sure that
b 2 - 4 ac is greater than or equal to zero before you compute the
roots. The flowchart is shown in Fig. 13-3. In this solution we use
two forms of the if . . .then . . .else statement. Study it carefully and
then load the program and run it.
10 REM* ROOTS*
20 PRINT "IF A QUADRATIC"
30 PRINT "EQUATION IS OF THE"
40 PRINT "FORM 0=A*X 2+B*X+C
50 PRINT "ENTER A, B, C"
60 INPUT A, B, C
70 D=B*B-4*A*C
80 IF A=0 THEN PRINT "A=0; NOT QUADRATIC.
REENTER VALUES" ELSE 100
90 GOTO 60
100 IF D >=0 THEN 120 ELSE PRINT "COMPLEX ROOTS:
CANNOT COMPUTE. REENTER VALUES."
110 GOTO 60
120 R1=(-B+SQR(D))/(2*A)
130 R2=(-B-SQR(D))/(2*A)
140 PRINT "COEFFICIENTS=";A;B;C
150 PRINT "ROOTS=";Rl;R2
160 END
To summarize, if A =0, the program displays message, then
continues to next statement. If A=0, the statement else 100 is read
and the program branches to statement 100. If D > =0, the program
branches to line 120. If D <0, the else message is displayed and the
program then continues to statement 110.
Run the program to find the roots of the equation x 2 +x — 6=0.
Then run the program again to test the decision with x+l=0 and
171
10 ( START J
20-60 /OUTPUT
/ INSTRUC- .
/ TIONS /
60 /
2
INPUT
VARIABLES/
EVALUATE
EXPRESSION UNDER
THE RADICAL
3»-4AC
NO (ELSE)
YES (THEN)
GOT0 100
<&K
YES (THEN)
GOTO 120
| NO (ELSE) 120
/ DISPLAY 7 130
ERROR /
MESSAGE/
EVALUATE
ROOTS
GOTO 60
150
/ PRINT
/ CO-
EFFICIENTS/
4 ROOTS /
160 ( END
Fig. 13-3.
172
x 2 +2x-l=0
RUN
IF A QUADRATIC EQ
EQUATION IS OF THE
FORM 0=A*XA2+B*X+C
ENTER A, B, C
?
1,1, -6(x z + x- 6)
COEFFICIENTS = 11-6
ROOTS=2 -3
RUN
IF A QUADRATIC
EQUATION IS OF THE
FORM 0=A*XA2+B*X+C
ENTER A, B, C
?
1, 2, 2(X 2 + 2X + 2)
COMPLEX ROOTS: CANNOT COMPUTE
REENTER VALUES
?
3,2,-1 (3X 2 + 2X- 1)
COEFFICIENTS=3 2 -
ROOTS= .333333333333 - 1
PSEUDOCODE
Pseudocode may be used as an alternative to flowcharting for
program design, the logic that determines the sequence in which
processing operations are carried out. In general, this technique
uses a code notation which has similarities to BASIC, but is not
quite the same.
In pseudocode, we are restricted to just three logic control
elements: sequence, selection, and iteration. In pseudocode, the
selection element is if . . . then . . . else and the iteration element is
perform . . . until. However, the overall structure of the pseudocode
need not show all the details of processing , just as a flowchart need
not show them.
Sequence requires no special notation. It is simply a conven-
tion that unless specified otherwise , operations are carried out from
top to bottom in the order written .
173
Chapter 14
ATARI Graphics and Sound
The ATARI 800 allows you to create graphics using BASIC com-
mands and different graphics modes. Using these commands, it is
possible to create graphics for games, illustrations, and diagrams.
Commands covered in this chapter will include:
GRAPHICS LOCATE PUT/GET
COLOR PLOT SET/COLOR
DRAWTO POSITION XIO
COMMANDS TO CONTROL THE GRAPHICS
Graphics
The graphics command is used to select one of the nine
graphics modes. Table 14-1 summarizes the nine modes and the
characteristics of each. The graphics command automatically opens
the screen, S:(the graphics window), as device #6. So when print-
ing text in the text window, it is not necessary to specify the device
code. The mode number must be positive and rounded to the
nearest integer. Graphics Mode is a full-screen display while
modes 1 through 8 are split screen displays. To override the
split-screen, add the characters +16 to the mode number (aexp) in
the graphics command. Adding 32 prevents the graphics command
from clearing the screen .
To return to Graphics Mode in the direct mode, press the
system reset button or type GR.O and press the return key.
Graphics Mode 0: This mode is the 1-color, 2-luminance
174
Table 14-1.
Modes and Screen Format.
SCREEN FORMAT
Gr.
Mode
Horiz.
Vert.
Vert.
Number
RAM
Mode
Type
(Rows)
(Col)
(Col)
01
Required
Split
Full
Colors
(Bytes)
Screen
Screen
TEXT
40
24
2
993
1
TEXT
20
20
24
5
513
2
TEXT
20
10
12
5
261
3
GRAPHICS
40
20
24
4
273
4
GRAPHICS
80
40
48
2
537
5
GRAPHICS
80
40
48
4
1017
6
GRAPHICS
160
80
96
2
2025
7
GRAPHICS
160
80
96
4
3945
8
GRAPHICS
320
160
192
'/!
7900
(brightness) default mode for the ATARI 800. It contains a 24 by 40
character screen matrix. The default margin settings at 2 and 39
allow 38 characters per line. Margins may be changed by poking
LMARGN and RMARGN (82 and 83). Some systems have different
margin default settings . The color of the characters is determined
by the background color. Only the luminance of the characters can
be different. To display characters at a specified location, use one of
the following two methods. Note: "sexp" denotes a string expres-
sion; "aexp" denotes an arithmetic expression. "Lineno" means line
number.
Method 1
lineno POSITION aexpl, aexp2 Puts cursor at location
specified by aexpl
and aexp2.
Specifies graphics mode .
Suppresses cursor.
Specifies character to be
printed .
Specifies where to print
character.
Start loop to prevent READY
from being printed. (GOTO)
same lineno.)
Press BREAK to terminate
loop.
Graphics is also used as a clear screen command either in the
direct mode or the deferred mode. It terminates any previously
lineno PRINT sexp
Method 2
lineno GR.O
lineno POKE 752,1
lineno COLOR ASC(sexp)
lineno PLOT aexpl,
aexp2
lineno GOTO lineno
175
selected graphics mode and returns the screen to the default mode
(graphics 0).
Graphics Modes 1 and 2: As defined in Table 14-1, these
two five-color modes are text modes. However, they are both
split-screen modes. Characters printed in Graphics Mode 1 are
twice the width of those printed in graphics 0, but are the same
height. Characters printed in Graphics Mode 2 are twice the width
and height of those in Graphics Mode 0. In the split-screen mode, a
print command is used to display characters in either the text
window or the graphics window. To print characters in the graphics
window, specify device #6 after the PRINT command.
Example: 100 GR.l
110 PRINT #6; "ATARI"
The default colors depend on the type of character input . The
following table defines the default color and color register used for
each type.
DEFAULT COLORS FOR SPECIFIC INPUT TYPES
Character Type Color Register Default Color
Upper case alphabetical
Orange
Lower case alphabetical
1
Light Green
Inverse upper case alphabetical
2
Dark Blue
Inverse lower case alphabetical
3
Red
Numbers
Orange
Inverse numbers
2
Dark Blue
Unless otherwise specified, all characters are displayed in
upper case noninverse form. To print lower case letters and
graphics characters, use a poke 756,226. To return to upper case,
use poke 756,224. In Graphics Modes 1 and 2, there is no inverse
video, but it is possible to get all the rest of the characters in four
different colors.
A split-screen display for Graphics Modes 1 and 2 is shown in
Fig. 14-1. The X and Y coordinates start at (upper left of screen).
The maximum values are the numbers of rows and columns minus 1
(see Table 14-1).
Example: GRAPHICS 1 + 16
Graphics Modes 3, 5, and 7: These three 4-color graphics
176
(X = 0)
(Y = 0)
X-coordinale
E:
Text
Window
(4 lines)
Border (size
depends on
individual TV's overscan)
Fig. 14-1. The graphics and text windows.
modes are also split-screen displays in their default state, but may
be changed to full screen by adding +16 to the mode number. Modes
3, 5, and 7 are alike except that modes 5 and 7 use more points
(pixels) in plotting, drawing, and positioning the cursor. The points
are smaller, thereby giving a much higher resolution than that in
modes 0, 1, and 2.
Graphics Modes 4 and 6: These graphics modes are like
modes 5 and 7 respectively except that they use only two colors,
and therefore use less memory.
Graphics Mode 8: This graphics mode gives the highest
resolution of all the modes. As it takes a lot of RAM to obtain this
kind of resolution , it can only accommodate a maximum of one color
and two different luminances.
Color (C): The value of the expression in the color statement
determines the data to be stored in the display memory and used by
all subsequent plot and drawto commands until the next color
statement is executed. The value must be positive and is usually an
integer from through 255. Nonintegers are rounded to the nearest
integer. The graphics-display hardware interprets this data in dif-
ferent ways in the different graphics modes. In Text Modes
through 2, the number can be from through 255 (8 bits) and
determines the character to be displayed and its color.
Tables 14-4 and 14-5 later in this chapter illustrate the internal
character set and the character/color assignment.
177
Graphics Modes 3 through 8 are not text modes, so the data
stored in the display RAM simply determines the color of each
pixel. Two-color or two-luminance modes require either or 1
(1-bit) and four-color modes require 0,1,2, or 3. The actual color
which is displayed depends on the value in the color register which
corresponds to the data of , 1 ,2 , or 3 in the particular graphics mode
being used. This may be determined by looking in Table 14-2, which
gives the default colors and the corresponding register numbers.
Colors may be changed by using the setcolor command described on
the following pages .
Note that when BASIC is first powered up, the color data is 0,
and when a graphics command (without +32) is executed, all of the
pixels are set to 0. Therefore, nothing seems to happen when the
plot and drawto commands are used in graphics 3 through 7 when no
color statement has been executed . Correct by doing a color 1 first .
Drawto: This statement causes a line to be drawn from the
last point displayed by a plot to the location specified by aexpl and
aexp2. The first expression represents the X coordinate and the
second represents the Y coordinate. The color of the line is the
same color as the point displayed by plot.
Locate: This command positions the invisible graphics cursor
at the specified location in the graphics window, retrieves the data
at that pixel , and stores it in the specified arithmetic variable . This
gives a number from to 255 for Graphics Modes through 2; or 1
for the 2-color graphics modes; and 0,1,2, or 3 for the 4-color
modes . The two arithmetic expressions specify the X and Y coordi-
nates of the point, locate is equivalent to:
POSITION aexpl, aexp2:GET #6, avar
Doing a print after a locate may cause the data in the pixel
which was examined to be modified. This problem is avoided by
repositioning the cursor and putting the data that was read back into
the pixel before doing the PRINT. The following program illus-
trates the use of the locate command.
10 GRAPHICS 3 + 16
20 COLOR 1
30 SETCOLOR 2,10,8
40 PLOT 10,15
50 DRAWTO 15,15
60 LOCATE 12, 15 ,X
70 PRINT X
178
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179
On execution, the program prints the data (1) determined by
the color statement which was stored in pixel 12, 15.
Plot: The plot command is used in Graphics Modes 3 through 8
to display a point in the graphics window. The aexpl specifies the
X-coordinate and the aexp2, the Y-coordinate. The color of the
plotted point is determined by the hue and luminance in the color
register determined by the last color statement executed. To
change this color register, and the color of the plotted point, use
setcolor. Points that can be plotted on the screen are dependent on
the graphics mode being used. The range of points begins at 1 and
extends to one less than the total number of columns (X-coordinate)
or rows (Y-coordinate) shown in Table 14-1.
Position: The position statement is used to place the invisible
graphics-window cursor at a specified location on the screen . This
statement can be used in all modes. Note that the cursor does not
actually move until an I/O command which involves the screen is
issued.
Put: In graphics work, put is used to output data to the screen
display. This statement works hand-in-hand with the position
statement. After a put, the cursor is moved to the next location on
the screen. Doing a put to device #6 causes the one-byte input to be
displayed at the cursor position. The byte is either an AT ASCII
code byte for a particular character or the color data.
Get: Is used to input the code byte of the character displayed at
the cursor position into the specified arithmetic variable. The val-
ues used in put and get correspond to the values in the color
statement. (Print and input may also be used.)
Doing a print after get from the screen may cause the data in
the pixel which was examined to be modified. To avoid this prob-
lem, reposition the cursor and put the data that was read, back into
the pixel before doing the print.
Setcolor: This statement is used to choose the particular hue
and luminance to be stored in the specified color register. The
parameters of the setcolor statement are defined below:
aexpl = Color register (0-4 depending on graphics mode) .
aexp2 = Color hue number (0-15. See Table 14-3).
aexp3 = Color luminance (must be an even number between
and 14; the higher the number, the brighter the dis-
play. 14 is almost pure white!)
The ATARI display hardware contains five color registers,
180
Table 14-3. Hue (Setcolor Command) Numbers and Colors.
Colors
Setcolor (aexp2) Numbers
Gray
Light orange (gold)
1
Orange
2
Red -orange
3
Pink
4
Purple-blue
6
Blue
7
Blue
8
Light blue
9
Turquoise
10
Green-blue
11
Green
12
Yellow-green
13
Orange-green
14
Light orange
15
Note: Colors will vary with type and adjustment of TV or monitor used.
numbered from through 4. The operating system (OS) has five
RAM locations (colorO through color4) where it keeps track of the
current colors. The setcolor statement is used to change the values
in these RAM locations. The setcolor statement requires a value
from to 4 to specify a color register. The color statement uses
different numbers because it specifies data which only indirectly
corresponds to a color register. This can be confusing, so ex-
perimentation and study of the various tables in this chapter is
recommended.
No setcolor commands are needed if the default set of five
colors is used. See Table 14-4. Although 128 different color-
luminance combinations are possible, not more than five can be
displayed at any one time . The purpose of the color registers and
setcolor statement is to specify these five colors.
A program illustrating Graphics Mode 3 and the commands
explained so far is shown below:
10 GRAPHICS 3
20 SETCOLOR 0,2,8: COLOR 1
30 PLOT 17,1: DRAWTO 17, 10: DRAWTO 9, 18
40 PLOT 19,1: DRAWTO 19, 18
50 PLOT 20,1: DRAWTO 20, 18
60 PLOT 22,1: DRAWTO 22, 10: DRAWTO 30,18
70 POKE 752,1
181
Table 14-4. Setcolor "Default" Colors."
Setcolor Defaults To Luminance Actual Color
(Color Register) color
2 8 Orange
1 12 10 Green
2 9 4 Dark blue
3 4 6 Pink or blue
4 Black
•"Default" occurs if no setcolor statement is used.
Note: Colors may vary depending upon the television
monitor type, condition, and adjustment.
80 PRINT: PRINT" ATARI PERSONAL COMPUTERS"
90 GOTO 90
The setcolor and color statements set the color of the points to
be plotted. The setcolor command loads color register with hue 2
and a luminance of 8. The next 4 lines plot the points to be dis-
played. Line 90 suppresses the cursor and line 100 prints the string
expression ATARI PERSONAL COMPUTERS in the next window.
Figure 14-2 shows how this program appears on the screen.
To assign colors to characters in Text Modes 1 and 2 , first look
up the character number in Table 14-5. Then look at Table 14-6 to
get the conversion of that number required to assign a color register
to it.
Example: Assign setcolor to lower case "r" in mode 2 whose
color is determined by register 0.
1. In Table 14-6, find the column and number for "r" (114-
column4) .
2. Using Table 14-7, locate column 4. Conversion is the
character number minus 32 (114-32=82).
3. Poke the Character Base Address (CHBAS) with 226 to
specify lower case letters or special graphics characters; that
is, poke 756,226 or CHBAS = poke CHEBAS, 226.
To return to upper case letters, numbers, and punctuation
marks, poke CHBAS with 224.
4. A print statement using the converted number (82) assigns
the lower case "r" to setcolor in mode 2.
XIO: This special application of the XIO statement fills an area
on the screen between plotted points and lines with a non-zero
value.
The following steps illustrate the fill process:
1. Plot bottom right corner (point 1).
182
2. Drawto upper right comer (point 2) . This outlines the right
edge of the area to be filled.
3. Drawto upper left corner (point 3).
4. Position cursor at lower left corner (point 4).
5. Poke address 765 with the fill color data (1,2, or 3).
This method is used to fill each horizontal line from top to
bottom of the specified area. The fill starts at the left and proceeds
across the line to the right until it reaches a pixel which contains
non-zero data. Fill cannot be used to change an area which has been
filled in with a non-zero value so the fill will stop. The fill command
will go into an infinite loop if a fill-with-zero command is attempted
on a line which has no non-zero pixels. Press the break key or the
system reset button to stop the fill if this happens.
The following program creates a shape and fills it with a data
(color) of 3. Note that the XIO command draws in the lines on the
left and bottom of the figure.
10 GRAPHICS 5+16
20 COLOR 3
30 PLOT 70,45
40 DRAWTO 50,10
50 DRAWTO 30,10
60 POSITION 10,45
70 POKE 765,3
80 XIO 18,#6,0,0,"S: "
90 GOTO 90
X-AXIS POINTS (COLUMNS)
2 3 4 3 K 7 B B 10 1112 1.1 14 13 IB I? 1BI92U 31 23 232423 26 2728293031 3233343536373631
DEVICE CODE -'S."
Screen
(Graphic* or Ten)
ATARI PERSONAL COMPUTERS
\/
(TEXT WINDOW)
DEVICE CODE "E.
Fig. 14-2. The ATARI symbol as produced by the program.
183
Table 14-5. Internal Character Set.
Column 1
Column 2
tt
CHR
tt
CHR
n
CHR
tt
CHR
Space
16
32
@
48
P
1 !
17
1
33
A
49
Q
2
>!
18
2
34
B
50
R
3
U
19
3
35
C
51
S
4
$
20
4
36
D
52
T
5
%
21
5
37
E
53
U
6
&
22
6
38
F
54
V
7
23
7
39
G
55
w
8
(
24
8
40
H
56
X
9
)
25
9
41
I
57
Y
10
*
26 :
42
J
58
z
11
+
27 ;
43
K
59
[
12
»
28
<
44
L
60
\
13
—
29
=
45
M
61
]
14
—
30
>
46
N
62
A
15
/
31
p
47
O
63
—
184
Column 3
Column 4
tt CHR
/r CHR
# CHR
tt CHR
64 Q
80 Q
96 Q
112 p
65 O
si H
97 a
113 q
66 n
82 Q
98 b
114 r
67 £J
83 O
99 c
115 s
68 O
84 Q
100 d
116 t
69 g)
85 (J
101 e
117 u
70 Q
86 n
102 f
118 v
71 O
37 Q
103 g
119 w
72 B
88 Q
104 h
120 x
73 P
89 (J
105 i
121 y
74 a
90 gj
106 j
122 z
75 B
9i °a
107 k
123 Q
76 Q|
92 Q
108 1
124 1
77 §|
93 Q
109 m
© it
125 W\
78
94 Q
110 n
126 "%
79 {J
95 Q
111
127 W
1. In mode these characters must
to be printed.
be preceded with an escape, CHR$(27),
185
Table 14-6. Character/Color Assignment.
Converson 1
Conversion 2
Conversion 3
Convention 4
MoOeO
'Setcotor 2
ff+32
ff+32
ff-32
None
Poke 756.224 Poke 756.226
Mode 1
Or
Mods 2
Setcotor
-$32
#+32
#-32
#-32
Selector l
None
#+64
#-64
Nona
Setcotor 2
#+160
#+160
#+86
ff+96
Selector 3
#+128
# + 192
#+64
ff+126
2. Luminance controlled by Setcotor 1.0. LUM
Graphic Control Characters: These characters are pro-
duced when the CTRL key is pressed with the alphabetic keys
shown in Fig. 14-3. These characters can be used to draw designs,
pictures , and the like in mode and in modes 1 , and 2 if CHBAS is
changed.
TEXT MODES CHARACTER PRINT PROGRAM
The following program prints the ATARI characters in their
default colors for Text Modes 0,1, and 2. When entering this
program, remember that the clear screen symbol " " is printed as
1 DIM A$(D
5 ?"}":REM CLEAR SCREEN
10 ? "GRAPHICS 0, 1, AND 2 (TEXT MODES)"
20 ? "DEMONSTRATION."
30 ?"DISPLAYS CHARACTER SETS FOR EACH MODE."
60 WAIT=1000:REM SUBROUTINE LINE NUMBER
70 CHBAS =756:REM CHARACTER BASE ADDRESS
80 UPPER=224:REM DEFAULT FOR CHBAS
90 LOWER=226:REM LOWER CASE LETTERS - GRAPH-
ICS
95 GOSUB WAIT
100 FOR L=0 TO 2
112 REM USE E: FOR GRAPHICS
115 IF L=0 THEN OPEN #1,8,0, "E":GOTO 118
116 REM USE S: FOR GRAPHICS
186
Table 14-7. Pitch
Values for Musical Notes.
High
C
29
Notes
B
31
A#orB t
33
A
35
G# or A b
37
G
40
F# or G •>
42
F
45
E
47
D#orE
50
D
53
C# or D t
57
C
60
B
64
A#orB
68
A
72
G#orA»
76
G
81
F# or G !•
85
F
91
E
96
D# or E *
102
D
108
CtforD 1,
114
Middle C
C
121
B
128
A# or B b
136
A
144
G# or A b
153
G
162
F#G k
173
F
182
Low Notes
D
193
DfforE 1,
204
D
217
C# or D k
230
C
243
Fig. 14-3. The keyboad graphics characters.
187
117 OPEN #1, 8, 0, "S:"
118 GRAPHICS L
120 PRINT "GRAPHICS ";L
130 FOR J=0 TO 7:REM 8LINES
140 FOR 1=0 TO 31 :REM 32 CHARS/LINE
150 K=32*J+I
155 REM DON'T DISPLAY "CLEAR SCREEN" OR "RE-
TURN"
160 IF K=ASC(")") OR K=155 THEN 180
165 IF L=0 THEN PUT #1, ASC (" "):REM ESCAPE
170 PUT #1,K:REM DISPLAY CHARS
180 NEXT I
190 PRINT #1;" " :REM END OF LINE
200 IF L<> 2 or J< >3 THEN 240
210 REM SCREEN GULL
220 GOSUB WAIT
230 PRINT #1;"}":REM CLEAR SCREEN
240 NEXT J
250 GOSUB WAIT
265 PRINT "LOW CASE AND GRAPHICS"
270 IF Lo0 THEN POKE CHBAS, LOWER:GOSUB WAIT
275 CLOSE #1
280 NEXTL
300 GRAPHICS 0:END
1000 REM WAIT FOR "RETURN"
1010 PRINT "HIT RETURN TO CONTINUE";
1020 INPUT A$
1030 RETURN
LIGHT SHOW PROGRAM
The following program demonstrates another aspect of ATARI
graphics. It uses Graphics Mode 7 for high resolution and the plot
and drawto statements to draw the lines. In line 20, the title will be
more effective if it is entered in inverse video using the ATARI logo
key.
10 FOR ST=1 TO 8:GRAPHICS 7
15 POKE 752,1
20 ? : ?" ATARI'S Special Light Show " rSETCOLOR 2 ,0 ,0
30 SETCOLOR 1, 2*ST,8:COLOR 2
40 FOR DR=0 TO 80 STEP ST
50 PLOT 0,0: DRAWTO 100,DR
188
60 NEXT DR: FOR N=l TO 800: NEXT N: NEXT ST
70 FOR N=l TO 2000: NEXT N'GOTO 10
UNITED STATES FLAG PROGRAM
This program involves switching colors to set up the stripes.
It uses Graphics Mode 7 plus 16 so that the display uses the full
screen. Note the correspondence between the color statements and
the setcolor statements . For fun and experimentation purposes , add
a sound statement and use a read/data combination to add "The Star
Spangled Banner" after line 470. Refer to next section to see how
this is done.
10 REM DRAW THE UNITED STATES FLAG
20 REM HIGH RESOLUTION 4-COLOR GRAPHICS, NO
TEXT WINDOW
30 GRAPHICS 7+16
40 REM SETCOLOR CORRESPONDS TO COLOR 1
50 SETCOLOR 0,4,4:RED =1
60 REM SETCOLOR 1 CORRESPONDS TO COLOR 2
70 SETCOLOR 1,0,14: WHITE=2
80 REM SETCOLOR 2 CORRESPONDS TO COLOR 3
90 BLUE =3:REM DEFAULTS TO BLUE
100 REM DRAW 13 RED & WHITE STRIPES
110 C=RED
120 FOR 1=0 TO 12
130 COLOR C
140 REM EACH STRIPE HAS SEVERAL HORIZONTAL
LINES
150 FORJ=0TO6
160 PLOT0,I*7+J
170 DRAWTO 159,I*7+J
180 NEXT J
190 REM SWITCH COLORS
200 C=C+1:IF C> WHITE THEN C=RED
210 NEXT I
300 REM DRAW BLUE RECTANGLE
310 COLOR BLUE
320 FOR 1=0 TO 48
330 PLOT 0,1
340 DRAWTO 79,1
350 NEXT I
360 REM DRAW 9ROWS OF WHITE STARS
189
370 COLOR WHITE
380 K=0:REM START WITH ROW OF 6 STARS
390 FOR 1=0 TO 8
395 Y=4+I*5
400 FOR J=0 TO 4: REM 5 STARS IN A ROW
410 X=K+5+J*14: GOSUB 1000
420 NEXT J
430 IF K< >0 THEN K=0: GOTO 470
440 REM ADD 6TH STAR EVERY OTHER LINE
450 X=5+5*14:GOSUB 1000
460 K=7
470 NEXT I
500 REM IF KEY HIT THEN STOP
510 IF PEEK (764) =255 THEN 410
515 REM OPEN TEXT WINDOW WITHOUT CLEARING
SCREEN
520 GRAPHICS 7+32
525 REM CHANGE COLORS BACK
530 SETCOLOR 0,4,4: SETCOLOR 1,0,14
550 STOP
1000 REM DRAW 1 STAR CENTERED AT X,Y
1010 PLOT X-l,Y:DRAWTO X+1,Y
1020 PLOT X,Y-1: PLOT X.Y+1
1030 RETURN
VIDEO GRAFFITI
This program requires a joystick controller for each player.
Each joystick has one color associated with it. By maneuvering the
joystick, different patterns are created on the screen. Note the use
of the stick and strig commands.
1 GRAPHICS
2 ? "VIDEO GRAFFITI"
5 REM X&Y ARRAYS HOLD COORDINATES
6 REM FOR UP TO 4 PLAYERS' POSITIONS.
7 REM COLR ARRAY HOLDS COLORS.
10 DIM A$(l) ,X(3) ,Y(3) ,COLR(3)
128 ? "USE JOYSTICKS TO DRAW PICTURES"
129 ? "PRESS BUTTONS TO CHANGE COLORS"
130 ? "INITIAL COLORS:"
131 ? "JOYSTICK 1 IS RED"
132 ? "JOYSTICK 2 IS WHITE"
190
133 ? "JOYSTICK 3 IS BLUE"
134 ? "JOYSTICK 4 IS BLACK (BACKGROUND)"
135 ? "BLACK LOCATION IS INDICATED BY A BRIEF
FLASH OF RED."
136 ? "IN GRAPHICS 8, JOYSTICKS 1 AND 3 ARE WHITE
AND 4 IS BLUE."
138 PRINT "HOW MANY PLAYERS (1-4)";
139 INPUT A$:IF LEN(A$)=0 THEN A$="l"
140 JOYMAX=VAL(A$)-l
145 IF JOYMAX<0 OR JOYMAX =4 THEN 138
147 PRINT "GRAPHICS 3 (40X24) , 5 (80X48) ,"
150 PRINT "7 (160X96), OR 8 (320X192)";
152 INPUT A$:IF LEN(A$)=0 THEN A$="3"
153 A=VAL(A$)
154 IF A=3 THEN XMAX=40:YMAX=24:GOTO 159
155 IF A=5 THEN XMAX=80:YMAX=48:GOTO 159
156 IF A=7 THEN XMAX=160:YMAX=96:GOTO 159
157 IF A=8 THEN XMAX=320:YMAX=192:GOTO 159
158 GOTO 147:REM A NOT VALID
159 GRAPHICS A+16
160 FOR 1=0 TO JOYMAX:X(I)=XMAX/2+I:Y(I)=YMAX/
2+LNEXT I: REM START NEAR CENTER OF SCREEN
161 IF A< >8 THEN 166
162 FORI=0TO2:COLR(I)=l:NEXTI
163 SETCOLOR 1,9,14:REM LT. BLUE
165 GOTO 180
166 FOR 1=0 TO 2:COLR(I)=I+l:NEXT I
167 SETCOLOR 0,4,6:REM RED
168 SETCOLOR 1,0,14:REM WHITE
180 COLR(3)=0
295 FOR J=0 TO 3
300 FOR 1=0 TO JOYMAX:REM CHECK JOYSTICKS
305 REM CHECK TRIGGER
310 IF STRIG(I) THEN 321
311 IF A< >8 THEN 320
312 COLR(I)=COLR(I)+l:IF COLR(I)=2 THEN COLR(I)=
0:REM 2-COLOR MODE
313 GOTO 321
320 COLR(I)=COLR(I)+l:IF COLR(I)>=4 THEN COLR(I)=
0:REM 4-COLOR MODE
321 IF J>0 THEN COLOR COLR(I) :GOTO 325
322 IF COLR(I)=0 THEN COLOR l:GOTO 325
191
323 COLOR 0:REM BLINK CURRENT SQUARE ON AND
OFF
325 PLOT X(I),Y(I)
330 JOYIN=STICK(I):REM READ JOYSTICK
340 IF JOYIN=15 THEN 530:REM NO MOVEMENT
342 COLOR COLR(I):REM MAKE SURE COLOR IS ON
344 PLOTX(I),Y(I)
350 IFJOYIN>=8THEN390
360 X(D=X(I)+1:REM MOVE RIGHT
370 IF X(I) > =XMAX THEN X(I) =0
380 GOTO 430
390 IFJOYIN>=12 THEN 430
400 X(I) =X(I)- 1 :REM MOVE LEFT
410 IF X(I)<0 THEN X(I)=XMAX- 1
430 IF JOYIN< >5 AND JOYIN< >9 AND JOYIN< > 13
THEN 470
440 Y(D=Y(D+1:IF Y(I)>=YMAXTHEN Y(I)=0: REMMOVE
DOWN
460 GOTO 500
470 IF JOYIN< >6 AND JOYIN< >10 AND JOYIN< > 14
THEN 500
480 Y(I)=Y(I)-1:IF Y(I)<0 THEN Y(I)=YMAX-1:REM
MOVE UP
500 PLOTX(I),Y(I)
530 NEXT I
535 NEXT J
540 GO TO 295
USING SOUND
In general, BASIC statements are used to generate musical
notes and sounds through the audio system of the television
monitor. Up to four different sounds can be "played" simultaneously
creating harmony . The sound statement can also be used to simu-
late explosions, whistles, and other interesting noises.
Sound: The sound statement causes the specified note to
begin playing as soon as the statement is executed. The note will
continue playing until the program encounters another sound
statement with the aexpl or an end statement. This command can
be used in either direct or deferred modes.
The sound parameters are described as follows:
192
aexpl= Voice. Can be 0-3, but each voice requires a separate
sound statement.
aexp2= Pitch. Can be any number between and 255. The
larger the number, the lower the pitch. Table 14-7
shows the pitch numbers for the various musical
notes ranging from two octaves above middle C to one
octave below middle C .
aexp3= Distortion. Can be any even number between and
14. A is used to create a "pure" tone whereas a 12
gives an interesting buzzer sound. A buzzing sound
can be produced using two separate sound commands
with the distortion value alternating between and 1 .
aexp4= Volume control. Can be between 1 and 15. Using a 1
creates a sound barely audible whereas a 15 is loud. A
value of 8 is considered normal. If more than one
sound statement is being used, the total volume
should not exceed 32 or an unpleasant "clipped" tone
will result.
The following example shows how to write a program that will
"play" the C scale.
10 READ A
20 IF A=256 THEN END
30 SOUND 0,A,10,10
40 FOR W=l TO 400:NEXT W
50 PRINT A
60 GOTO 10
70 END
80 DATA 29, 31, 35, 40, 45, 47, 53, 60, 64, 72, 81, 91, 96, 108,
121
90 DATA 128, 144, 162, 182, 193, 217, 243, 256
Note that the data statement in line 90 ends with a 256. A glance at
Table 14-7 will tell us that this is outside of the designated range.
The 256 is used as an end-of-data marker.
TYPE-A-TUNE PROGRAM
The following program turns the ATARI 800 into a single-scale
piano; that is, it assigns musical note values to the keys on the top
193
row of the computer keyboard . When you are using this program, do
not try to play harmony; press only one key at a time.
KEY MUSICAL VALUE
INSERT B
CLEAR B b (or A#)
A
9 A fc (or G#)
8 G
7 F# (or G k )
6 F
5 E
4 E b (or D#)
3 D
2 D k (or C#)
1 C
10 DIM CHORD(37),TUNE(12)
20 GRAPHICS 0:?:?" TYPE-A-TUNE PROGRAM"
25 ? :? "PRESS KEYS l-9,0,<,> TO PRODUCE NOTES.";
27 ? "RELEASE ONE KEY BEFORE PRESSING THE
NEXT."
28 ? "OTHERWISE THERE MAY BE A DELAY."
30 FOR X=l TO 37: READ A:CHORD(X)=A:NEXT X
40 FOR X=l TO 12:READ A:TUNE(X)=A:NEXT X
50 OPEN #1.4.0,"K:"
55 OLDCHR=-l
60 A=PEEK(764):IF A=255 THEN 60
63 IF A=OLDCHR THEN 100
65 OLDCHR=A
70 FOR X=l TO 12:IF TUNE(X)=A THEN SOUND 0,
CHORD(X),10,8:GOTO 100
80 NEXTX
100 I=INT(PEEK(53775)/4):IF (I/2)=INT(I/2) THEN 60
110 POKE 764,255:SOUND 0,0,0,0:OLDCHR=-1: GOTO 60
200 DATA 243,230,217,204,193,182,173,162,153,144,136,
128,121,114,108,102,96,91,85,81,76,72,68,64,60
210 DATA 57,53,50,47,45,42,40,37,35,33,31,29
220 DATA 31,30,26,24,29,27,51,53,48,50,54,55
To play "Twinkle, Twinkle Little Star" press the following
keys:
194
1,1,8,8,0,0,8 6,6,5,5,3,3,1
8,8,6,6,5,5,3 8,8,6,6,5,5,3
1,1,8,8,0,0,8 6,6,5,5,3,3,1
To play the "Marine's Hymn" press the following keys:
1,5,8,8,8,8,8,1,8
1,5,8,8,6,3,1
The following keys are pressed to play "London Bridge Is
Falling Down":
8,9,8,6,5,6,8 3,5,6 5,6,8
8,9,8,6,5,6,8 3,8,5,1
COMPUTER BLUES
This program generates random musical notes to "write" some
very interesting melodies for the programmed bass.
1 GRAPHICS 0:? :?" COMPUTER BLUES":?
2 PTR=1
3 THNOT=l
5 CHORD=l
6 PRINT "BASS TEMPO (1=FAST)";
7 INPUT TEMPO
8 GRAPHICS 2+16:GOSUB 2000
10 DIM BASE(3,4)
20 DIMLOW(3)
25 DIM LINEQ6)
26 DIMJAM(3,7)
30 FOR X=l TO 3
40 FOR Y=l TO 4
50 READ A:BASE(X,Y)=A
60 NEXTY
70 NEXTX
80 FOR X=l TO 3:READ A:LOW(X)=A
90 NEXTX
95 FOR X=l TO 16:READ A:LINE(X)=A:NEXT X
96 FOR X=l TO 3
97 FOR Y=l TO 7
98 READ A JAM(X,Y)=A:NEXT Y:NEXT X
100 GOSUB 500
195
110 T=T+1
115 GOSUB 200
120 GOTO 100
200 REM PROCESS HIGH STUFF
205 IF RND(0)<0.25 THEN RETURN
210 IF RND(0)<0.5 THEN 250
220 NT=NT+1
230 IFNT>7THENNT=7
240 GOTO 260
250 NT=NT-1
255 IFNT<1THENNT=1
260 SOUND 2JAM(CHORD,NT),10,NT*2
280 RETURN
500 REM PROCESS BASE STUFF
510 IF BASS=1 THEN 700
520 BDUR=BDUR+1
530 IF BDUR< > TEMPO THEN 535
531 BASS=1:BDUR=0
535 SOUND 0,LOW(CHORD),10,4
540 SOUND 1,BASE(CHORD),THNOT),10,4
550 RETURN
700 SOUND 0,0,0,0
710 SOUND 1,0,0,0
720 BDUR-BDUR+1
730 IF BDUR < > 1 THEN 800
740 BDUR=0:BASS=0
750 THNOT=THNOT+l
760 IF THNOT< >5 THEN 800
765 THNOT=l
770 PTR=PTR=1
780 IF PTR=17 THEN PTR=1
790 CHORD =LINE(PTR)
800 RETURN
1000 DATA 162,144,136,144,121,108,102,108,108,96,91,96
1010 DATA 243,182,162
1020 DATA 1,1,1,1,2,2,2,2,1,1,1,1,3,2,1,1
1030 DATA 60,50,47,42,40,33,29
1040 DATA 60,50,45,42,40,33,29
1050 DATA 81,68,64,57,53,45,40
2000 PRINT #6:PRINT #6:PRINT #6
2005 PRINT #6;" Computer"
196
2006 PRINT #6
2010 PRINT #6;" Blues"
2030 RETURN
197
Chapter 15
Programming in Machine Language
Machine language is the simplest form of computer language (for
the computer that is) . It consists of the binary instruction codes that
define the basic computer instruction. Each instruction is defined by
a unique binary code . When that code is interpreted by the com-
puter, the CPU and other sections of the computer carry out those
specific operations defined by that instruction.
Programs can be written in machine language by listing the
instructions in the proper sequence. Such a sequence of instructions
comprises the program that results in some worthwhile end result.
Machine language is by far the most difficult of all computer
languages to use . It not only requires a knowledge of the computer's
architecture and operation, but it is tedious and time-consuming.
Machine language programming, using binary numbers is also error
prone, and is therefore sometimes simplified by using octal or
hexadecimal codes instead of binary codes. Despite this improve-
ment, machine language programming is difficult. It is used for
writing only short, simple programs. When longer and more com-
plex programs are to be written , machine language programming is
abandoned in favor of assembly-language programming.
The ATARI 800 contains a 6502 microprocessor and it is
possible to call 6502 machine code subroutines from BASIC using
the USR function . Short routines may then be entered into a pro-
gram by hand assembly. Before the ATARI 800 returns to BASIC,
the assembly language routine must do a pull accumulator (PLA)
198
instruction to remove the number (N) of input arguments off the
stack. If this number is not 0, all of the input arguments must be
popped off the stack also using PLA.
The subroutine should end by placing the low byte of its result
in location 212 (decimal). It should then return to BASIC using an
RTS (Return from Subroutine) instruction. The BASIC interpreter
will convert the 2-byte binary number stored in locations 212 and
213 into an integer between and 65535 in floating-point format to
obtain the value returned by the USR function.
The ADR (address) function may be used to pass data that is
stored in arrays or strings to a subroutine in machine language . Use
the ADR function to get the address of the array of strings , and then
use this address as one of the USR input arguments.
We will take a look at an actual program very soon, but before
we do, let's review assembly language. Assembly-language pro-
gramming is the next step up from machine language. It still uses
the individual computer instructions for writing programs, but in-
stead of referring to these instructions by binary, octal, or
hexadecimal codes, each instruction is referred to by a shorthand
term. Each instruction is referred to by a short multiletter desig-
nator known as a mnemonic. For example, the instruction that
causes the addition of binary numbers is referred to by the
mnemonic ADD. The mnemonic for a store accumulator instruction
might be STA. These mnemonics eliminate the need to deal with
binary code. In addition, assembly-language programming provides
the ability to identify memory locations by symbolic names rather
than by actual address numbers. For example , the memory location
designated to hold the sum of an arithmetic operation might simply
be referred to as SUM. The actual memory address of that memory
location need not be used.
When you use assembly language, you will usually also use a
program called an assembler. The assembler is a translator pro-
gram that resides in memory and converts your program, written in
mnemonics and symbolic addresses, into machine code which can
be executed by the computer. The assembler looks at each
mnemonic operation code and symbolic address and converts it into
its appropriate binary operation code or address. Each mnemonic
typically results in the creation of one binary instruction.
Assembly language programming greatly speeds up and
simplifies the programming process. It eliminates many of the
complications of dealing with binary' numbers. Yet because assem-
bly language programs are capable of using the individual computer
199
instructions, powerful and efficient programs can be written.
The following program, Hexcode Loader, provides the means
of entering hexadecimal codes, converting each hexadecimal
number to decimal , and storing the decimal number in an array . The
array is then executed as an assembly-language subroutine. To use
this program, first enter it. Then save it on disk or cassette for
future use.
10 GRAPHICS 0:PRINT "HEXCODE LOADER PRO-
GRAM":PRINT
20 REM STORES DECIMAL EQUIVALENTS IN ARRAY A,
OUTPUTS IN PRINTED 'DATA STATEMENTS' AT
21 REM LINE NUMBER 1500
30 REM USER THEN PLACES CURSOR ON PRINTED
OUTPUT LINE, HITS "RETURN", AND ENTERS
31 REM REST OF BASIC PROGRAM INCLUDING USR
STATEMENT.
40 DIM A(50),HEX$(5)
50 REM INPUT, CONVERSION, STORAGE OF DATA.
60 N=0:PRINT"ENTER 1 HEX CODE. IF THERE ARE NO
MORE, ENTER 'DONE'.";
70 INPUT HEX$
80 IF HEX$="DONE" THEN N=999:GOTO 130
90 FOR 1=1 TO LEN(HEX$)
100 IF HEX$(I,I)<="9" THEN N=N*16+VAL(HEX$(I,
I)) -.GOTO 120
110 N=N*16+ASC(HEX$(I, I))-ASC("A")+10
120 NEXT I
130 PRINT N:C=C+1
140 A(C)=N
150 IF N<>999 THEN GOTO 60
190 REM PRINT OUT DATA LINE AT 1500
200 GRAPHICS 0: PRINT "1500 DATA";
210 C-0
220 C=C+1
230 IF A(C)=999 THEN PRINT "999":STOP
240 PRINT A(C);",";
250 A(C)=0
260 GOTO 220
300 PRINT "PUT CORRECT NUMBER OF HEX BYTES IN
LINE 1000.":STOP :REM TRAP LINE
200
999 REM ** EXECUTION MODULE *♦
1000 CLR :BYTES=0
1010 TRAP 300:DIM E$ (l),E(INT(BYTES/6)+l)
1030 FOR 1=1 TO BYTES
1040 READ A: IF A>255 THEN GOTO 1060
1050 POKE ADR(E$)+I,A
1060 NEXT I
1070 REM BASIC PART OF USER'S PROGRAM FOLLOWS
Once this much of the program has been typed, add your own
BASIC language part of the program. Start at line 1080 and include
the USR function that calls the machine-language subroutine. Some
sample programs follow.
Count the total number of hex codes to be entered and enter
this number on line 1000 when requested. If another number is
already entered, simply replace it.
Run the program and enter the hexadecimal codes of the
machine-level subroutine. Press the return key after each entry.
After the last entry, type done and press the return key.
Now the data line (1500) displays on the screen. It will not be
entered into the program until the cursor is moved to it and the
return key is pressed.
Add a program line 5 goto 1000 to bypass the hexcode loader
(or delete the hexcode loader through line 260). Now save the
completed program by using csave or save. It is important to save
the program before executing the part of the program containing the
USR call . A mistake in a machine-language routine may cause the
system to crash . If the system does hang up , press the system reset
button. If the system doesn't respond, turn power off and on again,
reload the program, and correct the mistake.
The following sample programs can each be entered into the
Hexcode Loader program. The first program prints NOTHING IS
MOVING while the machine-language program changes the colors.
The second simple program displays a BASIC graphics design and
then changes the colors.
1080 GRAPHICS 1+16
1090 FOR 1=1 TO 6
1100 PRINT #6
1110 PRINT #6
1120 PRINT #6
1130 PRINT #6
201
"nothing is moving!"
"NOTHING IS MOVING!"
"nothing is moving!"
"NOTHING IS MOVING!"
1140 NEXT I
1150 Q=USR(ADR(E$)+1)
1160 FOR 1=1 TO 25:NEXTI:GOTO 1150
After entering this program, change line 1000 to read:
1000 CLR:BYTES = 21
Type RUN and press the return key .
Now enter the hexadecimal codes column by column as shown .
68
2
A2
E8
E0
AC
3
C4
90
2
F5
BD
8C
C5
C7
2
2
9D
60
C4
BYTES = 21
When you have entered them all, type DONE and press the
return key. Now place the cursor after the last entry (999) on the
data line and press the return key.
Now run the program by typing GOTO 1000 and pressing the
return key, or if line 5 has been added, type RUN and press the
return key. Press the break key to stop the program and delete line
5.
The second program, which follows, should be entered in place
of the NOTHING IS MOVING program. Be sure to check the
BYTES = count in line 1000.
1080 GRAPHICS 7+16
1090 SETCOLOR 0,9,4
1100 SETCOLOR 1,9,8
1110 SETCOLOR 2,9,4
1120 CR=1
1130 FOR X=0 TO 159
1140 COLOR INT(CR)
1150 PLOT 80,0
1160 DRAWTO X,95
1170 CR=CR+0.125
1180 IF CR=4 THEN CR=1
202
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1190 NEXTX
1200 X=USR(ADR(E$)+1)
1210 FOR 1=1 TO 15:NEXT I
1220 GOTO 1200
Type RUN and press the return key.
Enter the hexadecimal codes for this program column by col-
umn.
68
2
A2
E8
EO
AC
2
C4
90
2
F5
BD
8C
C5
C6
2
2
9D
60
C4
BYTES = 21
When you have entered them all, type DONE and press the
return key. Now place the cursor after the last entry (999) on the
data line and press the return key.
Now run the program by typing GOTO 1000 and pressing the
return key, or add line 5 GOTO 1000, type RUN and press the
return key. Press the break key to stop program and delete line 5.
Table 15-1 illustrates an assembler subroutine used to rotate
colors which might prove useful. It is included here for your infor-
mation.
204
Chapter 16
Continuing Education
Computer technology isn't something you can learn quickly by
simply buying a microcomputer and studying a couple of books. Not
that it isn't possible to teach yourself this way , but you'll save a lot of
time if you start with some professional instruction.
Ideally, the best way to learn computer technology is to attend
one of the bona fide schools offering courses in computer science,
but for some of you, attending one of these colleges or schools may
not always be possible. You have to earn a living and, therefore,
full-time instruction is out of the question. You may find that a
home-study school can solve the problem. Location, working hours,
age, and educational background are not barriers for the serious,
highly-motivated home-study student. Furthermore, a person tak-
ing a home-study course can progress at his or her own pace— as
fast as he or she can master the lessons or as slowly and irregularly
(within reason) as necessary . Two correspondence schools offering
courses in computer technology include:
NRI
McGraw-Hill Continuing Education Center
3939 Wisconsin Avenue
Washington, DC 20016
and
National Technical Schools
4000 South Figueroa Street
Los Angeles, CA 90037
205
NRI
NRFs advanced course of study called the Professional Course
is designed to get qualified individuals into the exciting and rapidly
growing field of computer technology as quickly as possible. The
course was created by selecting the lessons from NRI's Master
Course that deal specifically with computers. The Professional
Course lesson texts are described in detail later on. The first lesson
in the course is "Introduction to Computers." The final lesson is
"Digital Troubleshooting Equipment."
The Professional Course lesson texts are supplemented with
thorough training on the Radio Shack TRS-80 model III microcom-
puter. This training is accomplished by interfacing the NRI Discov-
ery Lab with the TRS-80. The lab is the only equipment that is not
included in the tuition price of the course. If you've previously taken
an NRI electronics course perhaps you have a Discovery Lab al-
ready. If not, you can order the Discovery Lab through NRI for
$100.
The TRS-80 model III with 16K RAM is included in their
Professional Course training. This Radio Shack microcomputer
comes fully assembled and ready to use. It has many practical
applications that you can utilize after you've finished using it as a
training device. Training on the TRS-80 will give you the hands-on
experience you will need to move ahead in the world of microcom-
puter technology.
The NRI Professional Course in Microcomputer training pre-
pares you for the tremendous employment surge in the field of
computer service technicians— a growth that has soared from
63,000 back in 1978 and will reach 160,000 in 1990. This phe-
nomenal growth predicted by the U.S. Department of Labor,
Bureau of Labor Statistics will occur in an incredibly short
period— 154% growth in 12 years!
In the fields of computers and electronics, education is not only
necessary to get a job but also important to advance in your career.
NRI courses provide a sound technical education as a foundation for
entry level jobs at the technician level. In addition, NRI courses are
ideal for continuing education, the on-going process of refreshing
your fundamentals and gaining new knowledge of high technology
subjects . Continuing education will keep you competent and pro-
vide the kind of knowledge you will need to advance on the job or
land a new , better job . If you are serious about a technical career, an
NRI course can get you into one sooner and keep you going longer.
206
An NRI course can open many opportunities for earning extra
income in your spare time. Many NRI graduates have opened
part-time service shops in their homes to make extra money . That
opportunity and many others still exists today. Completion of an
NRI course could help you get an FCC license that would allow you
to do part-time service and installation work on mobile, marine,
aircraft, or CB radios. There is also a great need for part-time
technicians to repair microcomputers. Part-time and "moonlight-
ing" opportunities abound in electronics, and an NRI course will let
you take advantage of them. Part-time work will often open up
unexpected opportunities that blossom into a full-time business or a
rewarding career.
Electronics and computers are great hobbies and leisure-time
activities. There are literally thousands of individuals that enjoy
electronics as a general-interest, spare-time diversion. Electronics
is fun, interesting, challenging, and exciting. It involves a variety of
interests including amateur radio, CB, personal computing, hi-fi/
audio, model trains, radio control, and just plain experimenting, kit
building and the 1 ike . An NRI course can get you into a hobby quickly
and easily or enhance and enrich your present electronic hobby.
After all, a major part of any hobby is learning more about a subject
in your spare time. What better way than with a home-study course
such as those offered by NRI?
NATIONAL TECHNICAL SCHOOL
The subjects covered in NTS's microcomputer course are very
similar to those offered by NRI, except that NTS utilizes the Heath
89 computer instead of the Radio Shack TRS-80. In fact, when
sample lessons supplied by both schools were examined, each set of
lessons showed strong and weak points which were balanced-out by
similar inconsistencies in the lessons from the other school. Both
schools are approved by the Veterans Administration for GI train-
ing, and both have a staff of well-known professional consultants.
Courses for both schools are surprisingly complete, well
thought out, and well written . All the material was very easy to read
and understand, and the many illustrations created interest
throughout. Any person who finishes either of these courses and
who obtains a complete reference library (and knows how to use it)
should have the basic knowledge necessary to become a good
employee for any computer firm. The trained hobbyist will be able
to accomplish much more on his home computer than he or she
would otherwise.
207
TYPICAL CORRESPONDENCE LESSONS
The following is a sampling of the lessons and kits found in
typical correspondence courses. Of course, the exact contents will
vary from school to school, but these examples should give the
reader a good idea of what is in store for him or her.
Introduction to Electronics: You get off to a fast start with
an overview of the microcomputer industry . You get right to the
heart of the business with the study of what electricity is, how
electrical current is made to flow in a circuit, and the relationship
between current, voltage, and resistance.
How Electricity is Produced for Electronics: You explore
the important types of batteries such as dry cells, mercury cells,
manganese cells, lead-acid cells and nickle-cadmium cells. You are
then introduced to direct current (dc) and to alternating current (ac)
generators, and you carefully analyze how they work.
Current, Voltage, and Resistance: You are now ready for a
close-up examination of current, voltage, and resistance, discov-
ering how units of each are measured and how voltage sources act
when connected. You also learn how resistance limits the flow of
current. Since no discussion of electricity is complete without
carefully considering Ohm's Law (which is one of the most impor-
tant laws of electronics) , it is presented here in a readily under-
standable manner. You quickly learn how to use it to determine
circuit parameters.
Series and Parallel Circuits: In this lesson you get into
more complex circuits, learning the difference between series and
parallel circuits. You leam all about resistance in series circuits,
voltage drops, and the very important relationship between the
voltage drops in a series circuit and the source voltage . Building on
this knowledge , you learn how to find the resistance in a parallel
circuit. The lesson concludes with a study of voltage and current in
parallel circuits.
How Resistors are Used: Now that you have the basic
background to understand resistors and how they are used in cir-
cuits, you study the watt, the wattage rating of resistors, and the
transfer of power. You learn about resistor values, the color code
used to indicate the value of a resistor, and about resistors with
special characteristics, such as the temperature-sensitive ther-
mistor and the voltage-dependent varistor.
How Coils Are Used: You discover the different types of
coils, their uses and their basic function in electronic circuits. You
learn about magnetic circuits and compare them to circuits you have
208
already covered. You learn about inductive reactance and the op-
position that a coil offers to alternating current. You study Lenz's
Law for coils and learn how changing flux linkages can produce a
voltage. You study Kirchhoffs Voltage Law, and learn how Ohm's
Law is applied to simple circuits having resistance and inductance.
How Capacitors Are Used: In this lesson you study
capacitors (once called condensers) and examine the differences
between the various types (variable, paper, mica, ceramic and
electrolytic). You learn how these capacitors are made, and how
they are used . You learn how a capacitor stores electricity , and how
it works in ac circuits. You also learn about capacitive reactance.
How Resistors, Coils, and Capacitors Are Used To-
gether: Now that you understand resistance, capacitance, and
inductance, you see how circuits which contain all three can form
resonant circuits. You learn about both series-resonant and
parallel-resonant circuits. You learn how important resonant cir-
cuits are and how they are used in electronics.
How Transistors Work: You begin your study of the theory
behind transistors. You learn what a semiconductor is and how
semiconductor materials are combined to form diodes and transis-
tors. You learn about the junction diode, the Zener diode, the tunnel
diode , the pin diode , and the varactor diode . You study npn transis-
tors and pnp transistors and learn how field-effect transistors work.
By the time you have completed this lesson, you will know what a
MOSFET is, and how it works.
How Transistors Are Used: You learn about the three prin-
cipal transistor circuits: the common-base circuit, the common-
emitter circuit, and the common-collector circuit. You learn how
these circuits are used in amplifiers. You learn how the field-effect
transistor is used as an amplifier and how the gain of a dual-gate
field-effect transistor can be controlled.
Integrated Circuits: Here is an invaluable lesson showing
how transistors can be integrated into entire circuits and used in
computers and other equipment. This lesson is rounded out with a
study of both linear and digital integrated circuits.
Printed Circuit Boards: You get your first exposure to how
printed circuit boards are used to provide a convenient, low-cost,
and reliable means of mounting and interconnecting electronic com-
ponents . You learn how these boards are made and what materials
are used. You also leam how to lay out typical printed circuit boards
and how to repair them.
Periodic Waves and Time Constants: This lesson pro-
209
vides an in-depth study of the types of signals and circuits used in
control systems, computers, and other advanced electronic sys-
tems. You study periodic waveforms and pulses as well as the RC
and RL circuits which are used to shape the pulses and other
waveforms .
Cathode Ray Oscilloscopes: This lesson explains in detail
how the cathode-ray tube is combined with various circuits to form a
complete cathode-ray oscilloscope. You see how the oscilloscope is
used as a tool to observe and measure waveforms in circuits.
Relays and Relay Circuits: Now you analyze the construc-
tion and operation of various types of relays. You see how they
perform remote switching operations and are able to control large
amounts of power under the control and direction of small signals.
Regulated Power Supplies: You explore the basic half-
wave and full-wave rectifier circuits and elementary filter circuits.
You even get a full explanation of how active regulators are used to
provide pure dc for electronic circuits. You also become familiar
with the basic series and shunt regulators, as well as with the
special switching and other feedback regulators.
Transistor Amplifier Circuits: In this lesson you study
common transistor amplifier circuits in detail and see how various
configurations affect input and output impedance , voltage and power
gain, and phase shift. You also consider the differential amplifiers
and special compensating techniques used for stabilization.
How Oscillators Work: Now you can concentrate on how
transistors and integrated circuits can be used with LC circuits , RC
circuits, and crystals to produce oscillation. You study practical
circuits that generate the sinusoidal and pulse waveforms useful in
rf and computer timing applications. You investigate the operation
of several types of special digital circuits including the monostable
multivibrator and the astable multivibrator.
Introduction to Computers: You are now ready for a
close-up look at computers and their applications. You learn the
basic structure of computers, with special emphasis on the different
types of computers and their various circuits.
How Computers Are Used: The entire thrust of this lesson
is a well organized overview of how computers are used. A wide
variety of computer applications are discussed, paying particular
attention to their business and scientific applications. You explore
special topics such as simulation , time sharing , and process control .
Basic Computer Arithmetic: This lesson provides a review
of the decimal number system. It then teaches you what binary
210
numbers are and how they relate to decimal numbers. You go on to
study the forms used for binary addition, subtractions, multiplica-
tion and division in whole and fractional number applications . When
you complete this lesson you'll see the relationships between bi-
nary, octal, hexadecimal, and decimal numbers clearly.
Digital Codes and Computer Arithmetic: Now you begin a
close examination of fixed and floating point numbers, and the
methods used by computers to handle these numbers. You investi-
gate special codes such as the Gray code and the BCD code. You
leam about the complement representation of negative numbers in
binary and the popular ASCII code used by computers.
Digital Logic Circuits: Here you observe the basic transis-
tor inverter used as a switch to represent the two binary states, one
and zero. Basic, AND, and OR gates are covered using simple diode
logic. And, you leam all about the more complex logic elements
such as NAND, NOR, and EXCLUSIVE OR using RTL, DTL, TTL,
ECL, MOS, and CMOS logic elements. The characteristics of the
various logic families are discussed clearly and simply.
Boolean Algebra and Digital Logic: This lesson contains
an introduction to the special Boolean math used to analyze , design ,
and optimize combinational logic circuits. This is the math that
permits complex logic networks to be expressed in easily manipu-
lated equations which can be translated directly into optimized
circuits using simple logic gates.
Flip-Flops, Registers, and Counters: You now look at the
various types of flip-flop circuits used to store and manipulate
binary data. Here you leam that special registers are made up of
combinations of flip-flops to store and shift large numbers of binary
digits. You also see how other combinations of special flip-flops
form binary and BCD counter or divider circuits.
How Digital Logic Is Used: You gain an understanding of
how easily any complex logic function can be performed using only
basic NAND and NOR gates. The most widely used combinational
logic circuits are presented in such detail that you'll have no trouble
understanding them. They include encoders, multiplexers, demul-
tiplexers, comparators, and parity generators.
Computer Arithmetic Operations: You leam how the
arithmetic section of this computer uses logic to perform its func-
tions and operations on fixed and floating point numbers. You
become familiar with methods that are used to handle negative
numbers and you discuss hardware versus software handling of the
multiply and divide operations.
211
How Digital Computers Operate: You study the major
elements of the digital computer and discover how each section
depends on the others for proper operation and execution of stored
programs.
Register Transfer and Addressing: You learn the impor-
tance of registers in the computer. Special registers such as ac-
cumulators, index registers, program counters, and data registers
are discussed in detail. You find out how memory as well as input
and output can be considered to be registers when you are dealing
with the flow of data through the computer.
Computer Memories: Here you are introduced to the vari-
ous types of memories used in computers. You consider volatile as
well as nonvolatile memory , paying particular attention to semicon-
ductor memory and magnetic memory such as tape and disk.
Computer Input/Output: You learn how the I/O section of a
computer operates. In this lesson, special emphasis is placed on
becoming acquainted with some of the more popular types of
peripheral equipment used with computers.
Computer Peripheral Equipment: Peripheral equipment
makes up a large portion of any computer system so it is important
for you to learn how the different types of devices operate. This
lesson carefully surveys printers, magnetic tapes, floppy disks, and
terminals.
Data Conversion Systems: Analog-to-digital (A/D) and
digital-to-analog (D/A) conversion techniques are covered in detail.
Here you also get into related topics such as multiplexing and
sample-and-hold amplifiers. You round out this lesson by consider-
ing how these units are combined with computers to form various
types of data conversion and data acquisition systems.
Microprocessors and Microcomputers: The computer-
on-a-chip is the most powerful kind of electronic component . Called
the microprocessor, these devices are used in complete systems
called microcomputers. The elements that make up microcomput-
ers of all kinds are described, and examples of some popular mi-
croprocessors are shown. The ways that microprocessors are com-
bined with memory and input/output chips to create complete
computers for business and industrial applications are clearly and
concisely illustrated.
Microcomputer Applications: Already, millions of micro-
processors and microcomputers have been installed in consumer
products, industrial-process control systems, and small business-
es. In this lesson, several examples of popular applications are
212
illustrated. Examples include: (a) one-chip microcomputers in
high-volume consumer appliances; (b) single-board microcomput-
ers used in industrial control; (c) special-purpose computers de-
veloped for industrial applications like automatic bowling scoring
systems and telephone PABX's; and for small business computer
uses, including payroll, inventory control, and project scheduling.
Microprocessors and Support Circuits: To adequately un-
derstand the operation of a microprocessor, you must be thoroughly
familiar with the electrical characteristics of major products and the
support chips required to make them work in practical circuits.
Support circuits covered here include clock generators , bus buffers,
and status latches. Also pinpointed are the differences between
synchronous and asynchronous storage reference systems , and the
means by which these systems are supported by additional ICs.
Memories and Input/Output Ports: The structure of
memory systems and input/output ports are amazingly similar, and
are treated together. You learn the various ways the different
memory technologies are used. You also study the support circuitry
required to decode and select memory chips for both eight and
sixteen-bit word systems. You discover that some of the popular
methods of implementing simple serial and parallel I/O ports are
really special cases of memory architectures, and that the same
decoding methods apply.
Interface Circuits: Although input/output ports are essen-
tial to a microcomputer, most applications require specialized ways
of interfacing to unique sensors and actuators . In this lesson you
concentrate on those additional circuits and see how they work. You
explore the general rules that all interfaces follow and study some
specific examples of interfaces. Included in these examples are
audio cassette interfaces and simple analog interfaces for driving
conventional meters.
Register Transfers in Software: Now you are ready to
learn the simplest approach to programming any microcomputer.
This technique depends upon understanding all of the registers that
exist, and transferring data among these registers to achieve some
objective. You learn the techniques used for analyzing a computer's
instruction set and register complement. You also get detailed
step-by-step instructions for writing simple programs that use that
instruction set effectively.
Software and Programming: The important subject of
programming is introduced here. You get a general overview of
computer software including types of programming languages,
213
machine language, assembly language, higher-level languages,
higher-level compiler languages such as FORTRAN, and interpret-
ers such as BASIC, and programming and software systems.
Higher Level Languages: This lesson discusses the need
for the higher level languages and how they are used by computing
machines. Many popular languages are covered. A detailed expla-
nation , examples , and practice problems are included for the BASIC
and FORTRAN languages.
Programming Languages: Although programming can be
done in binary and assembly forms, the use of higher-level pro-
gramming languages is more popular and productive. In this lesson
you study the major features of the BASIC language, as well as some
features of the FORTRAN, PASCAL, and COBOL languages. Also
covered are other languages like FORTH and PL/M.
Development Environments: You begin a careful analysis
of the various ways to develop microcomputer hardware and
software, including simple kits, software development systems,
and complete multiterminal systems. You discover the differences
between cross-support and native-support products, and the need
for compatible program storage media in the cross-support envi-
ronment. You also become familiar with various software tools,
including assemblers, compilers, editors, interpreters and operat-
ing systems.
Digital Troubleshooting Equipment: This lesson care-
fully surveys the basic tools used with microcomputers that are
different from the more conventional electronics instrumentation.
You discover the advantages of using equipment such as the digital
delayed-sweep scope. You also learn how to use such special
troubleshooting equipment as portable front panels (such as the
Intel 820 Scope), logic state analyzers, and in-circuit emulation.
After studying topics like those described in this chapter,
you'll be one of the new breed of computer technician familiar not
only with programming and operations, but with the mechanical and
electronic nature of the expanding world of computers.
The following describes the various kits that currently accom-
pany correspondence courses in microcomputers and microproces-
sors. The examples are specifically from NRI's courses.
Kit No. 1: In your first training kit, you begin your study of
actual electronic circuits, the ones you need to know about to be the
new breed of computer specialist; the parts you need are included.
Even if you don't know one end of a soldering iron from the
other, you can use this kit . The instructions in your first training kit
214
take you step-by-step through ten carefully- written experiments
which develop your basic electronics skills. You learn how to
identify and install parts and make good solder connections to both
component terminals and printed circuit boards. It isn't long before
you recognize symbols and know how to construct circuits using
schematic diagrams. These fundamentals are your foundation for
sound troubleshooting and repair techniques.
Using your batteries, resistors, and the LED (light-emitting
diode) supplied as part of your kit, you work on actual circuits. You
see the effect of changing the resistance or voltage in the circuit as
you study both series and parallel circuits. Using NRI's new Action
Audio cassettes and specially coordinated diagrams, you learn the
operation and practical applications of your Beckman 3'/2 digit digi-
tal multimeter. You leam the professional way to take voltage,
current, and resistance measurements. The DMM becomes an
integral part of your training when you use it in your experiments to
demonstrate the basic fundamentals of electronics. You'll use it
later to measure power supply voltage and to verify the perfor-
mance of discrete components such as diodes, resistors, and tran-
sistors found on circuit boards in computers.
Specifications
Display:
3'/2 digit liquid crystal display (LCD) with a maximum read-
ing of 1999.
Power:
Single, standard 9-volt transistor battery.
Maximum Voltage:
1500 Vdc or peak ac.
Dimensions:
6.85" long x 3.65" wide x 1.8" high.
Weight:
16 ounces including battery.
Case:
High-impact ABS plastic, recessed switch and display.
Dc Volts:
100V to 1000V in 5 ranges.
Ac Volts:
100V to 1000V in 5 ranges.
Dc Current:
100 nA to 2A in 5 ranges.
Ac Current:
215
100 nA to 2A in 5 ranges.
Resistance:
0.1 to 20 M in 6 ranges.
Kit No. 2: You receive as part of your second kit, a profes-
sional hand-held digital multimeter. It's the basic, indispensible
tool for all computer specialists. You'll use this precision instru-
ment for all voltage, resistance and current measurements in the
experiments you perform in this kit, and you'll find it invaluable
after you've completed your course. You'll use it then to measure
voltages of power supplies and to verify the performance of discrete
components such as diodes, resistors, and transistors found on
most circuit boards in computers.
Using new audio cassettes and carefully coordinated diagrams
and schematics, you're personally talked through the operation and
practical applications of your digital multimeter (DMM). By fol-
lowing the step-by-step instructions on the cassette, you learn why
it is important to establish a reference point when taking measure-
ments and that a point in the circuit can be both positive and
negative.
You learn about voltage dividers and discover how a shunt
resistor, called a bleeder, can reduce variations in the output
voltage . You also learn how to check continuity by making voltage
measurements with your DMM. As you listen to the carefully-
sequenced instructions, you put the ohmmeter section of your
DMM into operation, learning how to trace circuits and measure
series and parallel resistor combinations.
Because you are working with NRFs Action Audio cassette,
your hands are free to perform the necessary operations and you can
make your visual observations at the same time. You avoid the
necessity of looking back and forth between printed instructions and
your digital multimeter, thus saving time and reinforcing your
learning.
Kit No. 3: This kit introduces you to ac circuits and the
particular components used in them . To perform the experiments in
this kit, you get a special chassis, a power transformer, an iron-core
choke (inductor), an ac line cord, resistors, capacitors, and miscel-
laneous hardware.
You explore the ac and dc characteristics of tubular and elec-
trolytic capacitors, learning first-hand about "RC time constants,"
capacitor leakage, and capacitive voltage dividers. You see how a
capacitor can pass ac current and block dc current .
You also examine in detail the characteristics of inductors in dc
216
and ac circuits and you determine how special resonant circuits can
be made by combining inductors and capacitors. You also look at
series and parallel resonance, seeing how these circuits can be
tuned by changing component values.
By the time you've completed this kit, you'll have no trouble
using your DMM to make both ac and dc current readings and
resistor measurements.
The special design of the kits give you a complete breadboard-
ing system for setting up and modifying prototype circuits, per-
forming tests , and evaluating electronic components . You are intro-
duced to the kind of high technology that's at the heart of today's
astounding electronics revolution.
You'll perform an incredible array of tests and experiments .
Even as you assemble the Lab, you perform 10 specific experiments
demonstrating the nature of electronic principles; then you perform
10 experiments using parts that range from transistors through
integrated circuits .
Specifications
Power Supply:
±10V unregulated
±5V regulated, 50 mA max
Function Generator:
Switch selectable waveform:
Triangle: 10V p-p
Square: to 5V TTL/CMOS compatible
Frequencies: 2Hz, 1Hz, 1kHz switch selectable.
Logic Indicators:
(4) identical LED circuits with drivers TTL/CMOS com-
patible inputs
Pushbuttons:
(1) debounced and buffered; TTL/CMOS compatible output
Slide Switch:
(1) or +5V with IK pullup resistor
Line Clock:
60 Hz buffered output, TTL/CMOS compatible
Other Features:
2- 5k free potentiometer
SPDT meter switch:
Breadboarding socket, solderless connections for ICs and
discrete components.
217
Kit No. 4: The successful operation of any computer depends
on a correctly operating power supply. In this kit you study the
fundamentals of power supplies.
You start by demonstrating counter-electromotive force and
showing that it can be used to produce a high voltage. Then you
study and compare the characteristics of the half-wave rectifier and
the full-wave bridge rectifier circuit. You demonstrate the former's
operation, see the effects of circuit defects, and compare its opera-
tion with that of a conventional full-wave rectifier. You go on to
observe how a simple filter increases the dc component and de-
creases the ac component of a rectifier's output . You also take a
good look at the operation of the pi filter and simulate a leaky
electrolytic capacitor to observe the problem of the power factor in
filters .
At this point you're ready to experiment with voltage doubler
rectifiers and observe how they produce twice the dc output voltage
of the basic half-wave and full-wave rectifiers. You go on to investi-
gate the operation of shunt voltage regultors using reverse-biased
Zener diodes. You examine the basic dc operation of npn and pnp
transistors. You wrap up this kit by studying the series voltage
regulator, and you actually assemble a dual polarity regulated
power supply on an etched circuit board. You'll use this power
supply in later parts of your course .
Kit No. 5: You're given detailed instruction for assembling the
major portion of your kits. Their special design gives you a com-
plete breadboarding system for setting up and modifying prototype
circuits , performing tests , and evaluating components . Later , you'll
use these kits to demonstrate the action of various computer func-
tions.
Connecting components is quick and easy with the universal
components matrix of your kits . You simply plug in component leads
and you're ready to conduct experiments.
The experiments in this kit cover transistor fundamentals , and
solid-state amplifiers and oscillators. You begin by demonstrating
different methods of biasing npn and pnp transistors, and you build
the basic amplifier types: common-emitter, common-collector, and
common-base .
Now having experimented with the basic circuits, you are
ready to use the transistor in more complex configurations. First
you observe the operation of a phase splitter; then the operation of a
common-emitter stage used as a switch and as a voltage amplifier.
You learn about direct-coupled (DC) and resistance-capacitance
218
coupled (RC) amplifiers, and you construct and verify the operation
of an LC oscillator circuit. You investigate the workings of two
types of RC oscillators: phase-shift and multivibrator.
You'll quickly discover that the field-effect transistor plays an
important role in computer electronics. Consequently, you round
out this kit by experimenting with the methods of FET biasing and
the three basic FET amplifiers: common-source, common-drift, and
common-gate .
Kit No. 6: Now you're ready to move into high tech advanced
electronic components and systems. To perform the experiments,
you receive 2 dual operational amplifier (op amp) integrated circuits
(ICs), 7 digital ICs, a 6-digit LED numeric display, an LED and
phototransistor, a unijunction transistor (UJT), and a silicon con-
trolled rectifier (SCR).
After you learn the basics of operational amplifier circuits you
use a special dual op-amp IC to build a versatile function generator.
This circuit provides you with a permanent signal source to furnish
variable-frequency square and triangular waves. You use an LED
level detector to see how these two waveforms differ.
You constuct and examine digital logic circuits— circuits just
like those that make up all computers. You work with the basic
digital storage element, the flip-flop and see how it can be used as a
frequency divider. You also learn how a binary-coded-decimal
(BCD) counter works, and how to connect the BCD output to a
decoder and numeric display unit.
219
Appendix A
Alphabetical Directory
of Basic Reserved Words
The following material is courtesy of ATARI, Inc., a Warner Communications
Company and is used with their permission.
Note: The period is mandatory after all abbreviated keywords.
RESERVED
WORD:
ABS
ADR
AND
ASC
ATN
BYE
CLOAD
CHR$
ABBREVIATION:
CLOA.
BRIEF SUMMARY
OF BASIC STATEMENT
Function returns absolute
value (unsigned) of the var-
iable or expression.
Function returns memory
address of a string.
Logical operator: Expression
is true only if both subex-
pressions joined by and are
true.
String function returns the
numeric value of a single
string character.
Function returns the arctan-
gent of a number or expres-
sion in radians or degrees.
Exit from BASIC and return
to the resident operating sys-
tem or console processor.
Loads data from Program Re-
corder into RAM.
String function returns a sin-
gle string byte equivalent to
a numeric value between
and 255 in ATASCII code.
220
RESERVED
WORD:
CLOG
CLOSE
CLR
COLOR
COM
CONT
ABBREVIATION:
CL.
C.
CON.
COS
CSAVE
DATA
DEG
DIM
D.
DE.
DI.
DOS
DO
?AWTO
DR,
END
ENTER
E.
BRIEF SUMMARY
OF BASIC STATEMENT
Function returns the base 10
logarithm of an expression.
I/O statement used to close a
file at the conclusion of I/O op-
erations.
The opposite of DIM:
Undimensions all strings;
matrices.
Chooses color register to be
used in color graphics work.
Same as DIM.
Continue. Causes a program
to restart execution on the
next line following use of the
liliLi key or encountering
a stop.
Function returns the cosine
of the variable or expression
(degrees or radians).
Outputs data from RAM to
the program recorder for
tape storage.
Part of read/data combi-
nation. Used to identify the suc-
ceeding items (which must be
separated by commas) as indi-
vidual data items.
Statement deg tells com-
puter to perform trigo-
nometric functions in degrees
instead of radians. (Default in
radians.)
Reserves the specified amount
of memory for matrix, array,
or string. All string variables,
arrays, matrices must be di-
mensioned with a dim state-
ment.
Reserved word for disk oper-
ators. Causes the menu to be
displayed. (See DOS Manual.)
Draws a straight line be-
tween a plotted point and
specified point.
Stops program execution; clos-
es files; turns off sounds. Pro-
gram may be restarted using
cont. (Note: end may be
used more than once in a pro-
gram.)
I/O command used to store
data or programs in untok-
enized (source) form.
221
RESERVED
WORD:
EXP
FOR
ABBREVIATION:
FRE
GET
GE.
GOSUB
GOS
GOTO
G.
RAPHICS
GR.
IF
INPUT
INT
LEN
LET
LE.
LIST
L.
LOAD
LO.
LOCATE
LOC
BRIEF SUMMARY
OF BASIC STATEMENT
Function returns e (2.7182818)
raised to the specified power.
Used with next to estab-
lish for/next loops. Intro-
duces the range that the loop
variable will operate in dur-
ing the execution of loop.
Function returns the amount
of remaining user memory
(in bytes).
Used mostly with disk opera-
tions to input a single byte of
data.
Branch to a subroutine begin-
ning at the specified line
number.
Unconditional branch to a
specified line number.
Specifies which of the eight
graphics modes is to be used.
Gr.O may be used to clear
screen.
Used to cause conditional
branching or to execute
another statement on the same
line (only if the first expres-
sion is true).
Causes computer to ask for
input from keyboard. Execu-
tion continues only when the
■■ | "" ;|, » key is pressed after input-
ting data.
Function returns the next low-
est whole integer below the
specified value. Rounding is
always downward, even
when number is negative.
String function returns the
length of the specified string
in bytes or characters (1 byte
contains 1 character).
Assigns a value to a specific
variable name. Let is option-
al in ATARI BASIC, and may be
simply omitted.
Display or otherwise output
the program list.
Input from disk, etc. into the
computer.
Graphics: Stores, in a speci-
fied variable, the value that
controls a specified graphics
point.
222
RESERVED
WORD:
LOG
LPRINT
NEW
NEXT
NOT
NOTE
ON
OPEN
OR
PADDLE
PEEK
PLOT
POINT
POKE
POP
POSITION
PRINT
ABBREVIATION:
LP.
NO.
0.
PL.
P.
POK.
POS.
PR. or :
BRIEF SUMMARY
OF BASIC STATEMENT
Function returns the natural
logarithm of a number.
Command to line printer to
print the specified message.
Erases all contents of user RAM.
Causes a for/next loop
to terminate or continue de-
pending on the particular
variables or expressions. All
loops are executed at least once.
A "1" is returned only if the
expression is NOT true. If it
is true, a "0" is returned.
See DOS/FMS Manual . . . used
only in disk operations.
Used with goto or gosub
for branching purposes. Mul-
tiple branches to different line
numbers are possible depend-
ing on the value of the ON
variable or expression.
Opens the specified file for in-
put of output operations.
Logical operator used be-
tween two expressions. If
either one is true, a "V is eval-
uated. A "0" results only if
both are false.
Function returns position of
the paddle game controller.
Function returns decimal
form of contents of specified
memory location (RAM or
ROM).
Causes a single point to be
plotted at the X,Y location
specified.
Used with disk operations
only.
Insert the specified byte into
the specified memory location.
May be used only with RAM.
Don't try to POKE ROM or
you'll get an error.
Removes the loop variable
from the gosub stack. Used
when departure from the
loop is made in other than
normal manner.
Sets the cursor to the speci-
fied screen position.
I/O command causes output
from the computer to the spec-
ified output device.
223
RESERVED
WORD:
ABBREVIATION:
BRIEF SUMMARY
OF BASIC STATEMENT
PTRIG
PUT
RAD
READ
REM
PU.
RE A.
R. or.
RESTORE
RES.
RETURN
RET
RND
RUN
RU.
SAVE
S.
SETCOLOR
SE.
SGN
SIN
SOUND
SO.
SQR
STATUS
ST.
Function returns status of the
trigger button on game con-
trollers.
Causes output of a single byte
of data from the computer to
the specified device.
Specifies that information is
in radians rather than de-
grees when using the trig-
onometric functions. Default
is to rad. (See Deg.)
Read the next items in the
data list and assign to spec-
ified variables.
Remarks. This statement does
nothing, but comments may
be printed within the pro-
gram list for future ref-
erence by the programmer.
Statements on a line that starts
with REM are not executed.
Allows data to be read
more than once.
Return from subroutine to
the statement immediately
following the one in which
gosub appeared.
Function returns a random
number between and 1, but
never 1.
Execute the program. Sets
normal variables, to 0, undims
array and string.
I/O statement causes data or
program to be recorded on
disk under filespec provided
with save.
Store hue and luminance color
data in a particular color reg-
ister.
Function returns +1 if value
is positive, if zero, —1 if neg-
ative.
Function returns trigonomet-
ric sine of given value (deg
or rad) .
Controls register, sound pitch,
distortion, and volume of a
tone or note .
Function returns the square
root of the specified value.
Calls status routine for speci-
fied device.
224
RESERVED
WORD:
STEP
STICK
STRIG
STOP
STR$
THEN
TO
TRAP
USR
VAL
XIO
ABBREVIATION:
STO.
BRIEF SUMMARY
OF BASIC STATEMENT
Used with for/next. De-
termines quality to be
skipped between each pair of
loop variable values.
Function returns position of
stick game controller.
Function returns 1 if stick
trigger button not pressed,
if pressed.
Causes execution to stop, but
does not close files or turn off
sounds.
Function returns a character
string equal to numeric value
given. For example: STR$(65)
returns 65 as a string.
Used with if: If expres-
sion is true, the then
statements are executed. If the
expression is false, control
passes to next line.
Used with for as in "FOR X
= 1 TO 10". Separates the loop
range expressions.
Takes control of program in
case of an INPUT error and
directs execution to a speci-
fied line number.
Function returns results
of a machine-language sub-
routine.
Function returns the equiva-
lent numeric value of a string.
General I/O statement used
with disk operations (see
DOS/FMS Manual) and in
graphics work (Fill).
225
Appendix B
Error Messages
ERROR
CODE NO. ERROR CODE MESSAGE
2 Memory Insufficient to store the statement or the
new variable name or to dim a new string variable.
3 Value Error: A value expected to be a positive in-
teger is negative, a value expected to be within a
specified range is not.
4 Too Many Variables: A maximum of 128 different
variable names is allowed. (See Variable Name
Limit.)
5 String Length Error: Attempted to store beyond the
DIMensioned string length.
6 Out of Data Error: Read statement requires more
data items than supplied by DATA statement(s).
7 Number greater than 32767: Value is not a posi-
tive integer or is greater than 32767.
8 Input Statement Error: Attempted to input a
non-numeric value into a numeric variable.
9 Array or String DIM Error: Dim size is greater
than 32767 or an array/matrix reference is out of the
range of the dimensioned size, or the array/matrix or
string has been already dimensioned, or a reference
has been made to an undimensioned array or string.
10 Argument Stack Overflow: There are too many
gosubs or too large an expression.
1 1 Floating Point Overflow/Underflow Error:
Attempted to divide by zero or refer to a number
larger than 1 x 10 98 or smaller than 1 x 10" 99 .
12 Line Not Found: A gosub, goto, or then ref-
erenced a non-existent line number.
13 No Matching For Statement: A next was en-
countered without a previous for, or nested for/
226
ERROR
CODE NO. ERROR CODE MESSAGE
next statement do not match properly. (Error is re-
ported at the next statement, not at FOR).
14 Line Too Long Error: The statement is too com-
plex or too long for BASIC to handle.
15 Gosub or For Line Delected: A next or return
statement was encountered and the corresponding
for or gosub has been deleted since the last run.
16 RETURN Error: A return was encountered with-
out a matching gosub.
17 Garbage Error: Execution of "garbage" (bad RAM
bits) was attempted. This error may indicate a
hardware problem, but may also be the result of faulty use
of poke. Try typing NEW or powering down, then
re-enter the program without any poke commands.
18 Invalid String Character: String does not start with
a valid character, or string in val statement is not a
numeric string.
Note: The following are input/output errors that re-
sult during the use of disk drivers, printers, or
other accessory devices. Further information is
provided with the auxiliary hardware.
19 Load program Too Long: Insufficient memory re-
mains to complete load.
20 Device Number Larger than 7 or Equal to 0.
21 LOAD FILR ERROR: Attempted to load a nonload
file.
128 BREAK Abort: Use hit the Hm key during I/O
operation
129 IOCB 1 already open
130 Nonexistent Device was specified.
131 IOCB Write Only. Read command to a write-only
device (Printer).
132 Invalid Command: The command is invalid for this
device.
133 Device or File not Open: No open specified for the
device.
134 Bad IOCB Number: Illegal device number.
135 IOCB Read Only Error: Write command to a
read-only device.
136 EOF: End of File read has been reached. (NOTE:
This message may occur when using cassette files.)
137 Truncated Record: Attempt to read a record longer
than 256 characters.
138 Device Timeout. Device doesn't respond.
139 Device NAK: Garbage at serial port or bad disk
drive.
140 Serial bus input framing error.
141 Cursor out of range for particular mode.
142 Serial bus data frame overrun.
143 Serial bus data frame checksum error.
144 Device done error (invalid "done" byte): Attempt to
write on a write-protected diskette.
227
ERROR
CODE NO. ERROR CODE MESSAGE
145 Read after write compare error (disk handler) or
bad screen mode handler.
146 Function not implemented in handler.
147 Insufficient RAM for operating selected graphics
mode.
160 Drive number error.
161 Too many OPEN files (no sector buffer available).
162 Disk full (no free sectors)
163 Unrecoverable system data I/O error.
164 File number mismatch: Links on disk are messed
up.
165 File name error.
166 Point data length error.
167 File locked.
168 Command invalid (special operation code) .
169 Directory full (64 files).
170 File not found.
171 Point invalid.
10CB refers to input/output control block. The device number is the same as the
IOCB number.
228
Appendix C
ATASCII
Character Set
A
v
.#,
4
V
4@
>
/
O
13
D
a
26
1A
1
1
O
14
E
a
27
IB
a
2
2
D
15
F
a
28
1C
o
3
3
a
16
10
B
29
ID
o
4
4
o
17
11
13
30
IE
o
5
5
a
18
12
a
31
IF
Q
6
6
Q
19
13
O
32
20
Space
7
7
G9
20
14
a
33
21
!
8
8
B
21
15
o
34
22
"
9
9
B
22
16
35
23
a
10
A
a
23
17
8
36
24
$
11
B
B
24
18
a
37
25
%
12
C
a
25
19
o
38
26
Sf
229
d s
39
27
'
40
28
(
41
29
)
42
2A
•
43
2B
+
44
2C
•
45
2D
-
46
2E
47
2F
/
48
30
49
31
l
50
32
2
51
33
i
52
34
■1
53
35
5
54
36
K
55
37
7
56
38
S
57
39
9
58
3A
59
3B
1
60
3C
<
61
3D
=
230
62
3E
>
63
3F
?
64
40
@
65
41
A
66
42
B
67
43
C
68
44
D
69
45
E
70
46
F
71
47
G
72
48
H
73
49
1
74
4A
J
75
4B
K
76
4C
L
77
4D
M
78
4E
N
79
4F
O
80
50
1>
81
51
«
82
52
K
83
53
S
84
54
T
85
55
u
86
56
V
87
57
w
88
58
X
89
59
V
90
5A
z
91
5B
t
92
5C
\
93
5D
]
94
5E
A
95
5F
-
96
60
a
97
61
a
98
62
b
99
63
c
100
64
d
101
65
e
102
66
f
103
67
g
104
68
h
105
69
i
106
6A
J
107
6B
k
A A /
m A/
*/
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
1(59
170
171
172
173
174
175
176
9A
9B
9C
9D
9E
9F
A0
Al
A2
A3
A4
A5
A6
A7
A8
A9
AA
AB
AC
AD
AE
AF
BO
IEOLI
i. ii" i J
231
A
4 /
J /
& J
177
Bl
200
C8
223
DF
178
B2
201
C9
224
EO
179
B3
202
CA
225
El
180
B4
203
CB
226
E2
181
B5
204
CC
227
E3
182
B6
205
CD
228
E4
183
B7
206
CE
229
E5
184
B8
207
CF
230
E6
185
B9
208
DO
231
E7
186
BA
209
Dl
232
E8
187
BB
210
D2
233
E9
188
BC
211
D3
234
EA
189
BD
212
D4
235
EB
190
BE
213
D5
236
EC
191
BF
214
D6
237
ED
192
CO
215
D7
238
EE
193
CI
216
D8
239
BF
194
C2
217
D9
240
FO
195
C3
218
DA
241
Fl
196
C4
219
DB
242
F2
197
C5
220
DC
243
F3
198
C6
221
DD
244
F4
199
C7
222
DE
245
F5
232
254 FE LU '''«»'»
255 FF \V\ Si»'
See Appendix H tor a usee program thai performs decimal. hexadecimal convert)
1. atascii stands for "ATARI ASCII". Letters and numbers have ihe same values as iho.se in ASCII, bul
some of the special characters are diifereni.
2. Except as shown, characters from 128-255 are reverse colors of 1 to 127.
3. Add 32 to upper case code to get lower case code lor same letter.
4. To get ATASCII code, tell computer (direct model to PRINT ASC I" "*) Fill blank with letter,
character, or number of code. Must use the quotes!
233
Appendix D
ATARI 400/800 Memory Map
ADDRESS CONTENTS
Decimal Hexadecimal
65535
57344
FFFF
E000
OPERATING SYSTEM ROM
57343
55296
DFFF
D800
FLOATING POINT ROM
55295
53248
D7FF
D000
HARDWARE REGISTERS
53247
49152
CFFF
C000
NOT USED
49151
40960
BFFF
A000
CARTRIDGE SLOT A
(may be RAM if no A or B cartridge)
40959
32768
9FFF
8000
CARTRIDGE SLOT B
(may be RAM if no B cartridge)
RAMTOP (MSB)
32767 7FFF (7FFF if 32K system)
DISPLAY DATA (size varies)
234
ADDRESS CONTENTS
Decimal Hexadecimal
DISPLAY LIST (size varies)
31755 7CIF (7C1F if 32K system, (GRAPHICS 0)
OS MEMTOP
FREE RAM
(si/p varies)
[SIC MEMTOP
^ 1 bt
10880 2A80
BASIC program, buffers, tables, run-time stack.
(2A80 if DOS, may vary)
U
I OS MEMLO
BASIC LOMEM
10879 2A7F DISK OPERATING SYSTEM (2A7F-700)
9856 2680 DISK I/O BUFFERS (current DOS)
9855
4864
267F
1300
DISK OPERATING SYSTEM RAM (current DOS)
4863
1792
12FF
700
FILE MANAGEMENT SYSTEM RAM (current DOS)
1791
1536
6FF
600
FREE RAM
1535
1406
5FF
57E
FLOATING POINT (used by BASIC)
1405
1152
57D
480
BASIC CARTRIDGE
1151
1021
47F
3FD
]
OPERATING SYSTEM RAM (47F-200)
CASSETTE BUFFER
1020
1000
3FC
3E8
RESERVED
999
960
3E7
3C0
PRINTER BUFFER
959
832
831
512
3BF
340
33F
200
]
]
IOCB's
MISCELLANEOUS OS VARIABLES
511
256
IFF
100
HARDWARE STACK
255
212
FF PAGE ZERO
D4 FLOATING POINT (used by BASIC)
235
ADDRESS CONTENTS
Decimal Hexadecimal
211 D3
210 D2
BASIC or CARTRIDGE PROGRAM
209 Dl
208 UO
FREE BASIC RAM
207 CF
203 CB
FREE BASIC AND ASSEMBLER RAM
202
CA
176
BO
128
80
FREE ASSEMBLER RAM I BASIC
ASSEMBLER ZERO PAGE ( ZERO PAGE
127 7F
OPERATING SYSTEM RAM
As the addresses for the top of RAM , OS , and BASIC and the ends of OS and BASIC
van' according to the amount of memory , these addresses are indicated by pointers.
236
Appendix E
Derived Functions
Secant
Cosecant
Inverse Sine
Inverse Cosine
Inverse Secant
Inverse Cosecant
Inverse Cotangent
Hyperbolic Sine
Hyperbolic Cosine
Hyperbolic Tangent
Hyperbolic Secant
Hyperbolic Cosecant
Hyperbolic Cotangent
Inverse Hyperbolic Sine
Inverse Hyperbolic Cosine
Inverse Hyperbolic Tangent
Inverse Hyperbolic Secant
Inverse Hyperbolic Cosecant
Inverse Hyperbolic Cotangent
Derived Functions
Derived Functions in Terms
of ATARI Functions
SEC(X)=l/COS(X)
CSC(X)=1/SIN(X)
ARCSIN(X)=ATN(X/SQR(-X»X+1))
ARCC0S(X)=-ATN(X/SQR(-X«X+1)+
CONSTANT
ARSEC(X)=ATN(SQR(X*X- 1))+(SGN(X- 1)«
CONSTANT
ARCCSC(X)=ATN(1/SQR(X»X-1))+(SGN(X-1)
•CONSTANT
ARCCOT(X)=ATN(X)+CONSTANT
SINH(X)=(EXP(X)-EXP(-X))/2
COSH(X) =(EXP(X) +EXP(- X))/2
TANH(X)=- EXP(- X)/(EXP(X)+EXP(- X))*2+l
SECH(X) =2/(EXP(X) +EXP(- X))
CSCH(X) =2/(EXP(X)- EXP(- X))
COTH(X) =EXP(- X)/(EXP(X)- EXP(- X)>2+1
ARCSINH(X) =L0G(X+SQR(X»X+1))
ARCCOSH(X)+LOG(X+SQR(X»X- 1))
ARCTANH(X)=LOG((l+X)/(l- X))/2
ARCSECH(X)=L0G((SQR(-X*X+1)+1/X)
ARCCSCH(X)=LOG((SGN(X)*SQR(X*X+l)+l)
/X)
ARCCOTH(X)=LOG((X+l)/(X- 1))/2
Notes:
1. If in RAD (default) mode, constant = 1.57079633
If in DEG mode, constant = 90.
2. In this chart, the variable X in parentheses represents the value or expression to
beevaluated by the derived function. Obviously, any variable name is permissi-
ble, as long as it represents the number or expression to be evaluated.
237
Appendix F
Printed Versions
of Control Characters
The cursor and screen control characters can be pl aced in a string in a program or
used as a direct mode statement by pressing the |£Ug key before entering the
character from the keyboard. This causes the special symbols which are shown
below to be displayed.
PRESS AND
HOLD PRESS
238
Appendix G
Memory Locations
Note: Many of these locations are of primary interest to expert programmers and are
included here as a convenience . The labels given are used by ATARI programmers to
make programs more readable.
DECIMAL HEXADECIMAL COMMENTS
LABEL LOCATION LOCATION AND DESCRIPTIONS
Highest location used by
BASIC (LSB, MSB)
TV frame counter (1/60
sec.) (LSB, NSB, MSB)
Noisy I/O Flag (0=quiet)
Attract Mode Flag
(128=Attract mode)
Left, Right Margin (De-
faults 2, 39)
Current cursor row
(graphics window) .
Current cursor column
(graphics window)
Previous cursor row
(graphics window).
Previous cursor column
(graphics window).
Data under cursor (graph-
ics window unless mode
0).
Cursor row to which
drawto will go.
Cursor column to which
drawto goes .
Actual top of memory
(number of pages).
APPMHI
14,15
DE
RTCLOK
18,19,20
12,13,14
SOUNDR
65
77
41
LMARGIN,
RMARGIN
ROWCRS
82,83
84
52,53
54
COLCRS
85,86
55,56
OLDROW
90
5A
OLDCOL
91,92
5B
93
sc
NEWROW
96
60
NEWCOL
97,98
61,62
RAMTOP
106
6A
239
LABEL
LOMEM
MEMTOP
STOPLN
ERRSAV
PTABW
FRO
RADFLG
LPENH
DECIMAL
LOCATION
128,129
144,145
186,187
195
201
212,213
251
564
HEXADECIMAL
LOCATION
80,81
90,91
BA.BB
D4.D5
i'B
234
LPENV
TXTROW
TXTCOL
565
656
657,658
235
290
291,292
COLORO
COLORl
COLOR2
COLOR3
COLOR4
MEMTOP
708
709
710
711
712
741,742
2C4
2C5
2C6
2C7
2C8
2E5.2E6
MEMLO
CRSINH
743,744
752
2E7.2E8
2F0
CHACT
755
2F3
CHBAS
756
2F4
ATACHR
CH
763
764
2FB
2FC
FILDAT
765
2FD
DSPFLG
766
2FE
SSFLAG
767
2FF
HATABS
794
31A
COMMENTS
AND DESCRIPTIONS
BASIC low memory
pointer.
BASIC top of memory
pointer.
Line number at which
stop or trap occurred
(2-byte binary number).
Error number.
Print tab width
(defaults to 10)
Low and high bytes of
value to be returned to
BASIC from USR function.
RAD/DEG flag (0 = ra-
dians, 6 = degrees).
Light Pen* Horizontal
value.
Light Pen* Vertical value.
Cursor row (text window)
Cursor column (text
window)
Color Register
Color Register 1
Color Register 2
Color Register 3
Color Register 4
OS top of available
user memory pointer
(LSB, MSB)
OS low memory pointer
Cursor inhibit (0 = cursor,
on , 1 = cursor off)
Character mode register
4 = vertical reflect; 2 =
normal; 1 = blank)
Character base register
(defaults to 224) (224 =
upper case, 226 = lower
case characters)
Last ATASCII character.
Last keyboard key
pressed; internal code;
(255 clears character).
Fill data for graphics
Fill (XIO).
Display Flag (1 =
display control character) .
Start/Stop flag for paging
= n ormal listing) Set by
GE9 1.
Handler address table (3
bytes/handler)
240
DECIMAL
HEXADECIMAL
COMMENTS AND
LABEL
LOCATION
LOCATION
DESCRIPTION
IOCB
832
340
I/O control blocks (16
bytes/IOCB)
1664-1791
680-6FE
Spare RAM
CONSOL
53279
D01F
Console switches (bit 2 =
Option; bit 1 = Select; bit
= Start. Poke 53279,
before reading. =
switch pressed.)
PORTA
54016
D300
PIA Port A Controller
Jack I/O ports.
PORTB
54017
D301
PIA Port B Initialized to
hex 3C.
PACTL
54018
D302
Port A Control Register
(on Program Recorder 52
= ON, 60 = OFF).
PBCTL
54019
D303
Port B control register.
SKCTL
53775
D20F
Serial Port control reg-
ister. Bit 2 = (last key
still pressed).
• Future product.
241
Appendix H
Glossary of Microcomputer Terms
Address: A location in memory, usually specified by a two-byte
number in hexadecimal or decimal format.
Algorithm: A precisely defined set of rules or a structured proce-
dure which provides the solution to a problem in a finite number
of steps. An example follows:
Compute the value of a polynomial of the form
f(9x)=ax n + bx"- 1 + ex"" 2 . . .
For n=5 we can write the following algorithm:
f(x)=(((((a)x+b)x+c)x+d)x+e)x+f
This algorithm indicates that the computation can be done by
repeating a multiply-and-add step five times.
Alphanumeric: The capital letters A-Z and the numbers 0-9,
and/or combinations of letters and numbers. Specifically
excludes graphics symbols, punctuation marks, and other special
characters .
ALU: Abbreviation for arithmetic-and-logic unit.
Analog computer: A computer that uses variables represented by
voltages, currents, or other parameters whose values are
analogous to the quantitative magnitude of the variables.
Analog-to-digital conversion: The process of representing pre-
cisely a varying voltage or current by a series of discrete pulses
when the varying voltage or current itself is an analog of some
other form of information. Analog-to-digital conversion
techniques are required to convert any information that is in
242
Analog-to-digital conversion— Assembly language
analog form into the digital form required by the microcomputer.
Analog data is frequently encountered in data acquisition as
voltage from a transducer, potentiometer, or other sensor of
physical data.
Analyzer: A routine to analyze a program. It usually consists of
summarizing references to storage locations and tracing jump
sequences .
AND: A logic operation that states that if A and B are both state-
ments, then A AND B is true if both statements are true, but it is
false if either one or both statements are false. Truth is usually
expressed by the value 1 , while is used to indicate a false state .
The AND operator is usually represented by a centered dot
A- B
or by no sign
AB
An inverted u is sometimes used to denote the logical product
AnB
Finally, the standard multiplication sign may be used to express
the AND function
A x B
Array: A one dimensional set of elements that can be referenced
one at a time or as a complete list by using the array variable
name and one subscript. Thus the array B, element number 10
would be referred to as B(10). Note that string arrays are not
supported by BASIC , and that all arrays must be DIMensioned . A
matrix is a two dimensional array.
ASCII keyboard: A typewriter terminal keyboard laid out in a
specific format and containing the character symbol buttons and
function switches required to generate signals representing the
127 different character variations of the American Standard Code
for Information Interchange.
Assembler: A computer program that is used to translate symbolic
language into machine language . A typical program supplied by a
microcomputer manufacturer is loaded using PROM or ROM
chips and then executed to perform the assembly operation.
Assembly language: A language that uses words, statements,
and phrases to produce machine instructions. Most micro-
processor programs are written as a series of source statements
that are then translated using an assembly language into machine
code.
243
ATASCn— Binary Load
ATASCII: Stands for ATARI American Standard Code for Infor-
mation Interchange . It is the method of coding used to store text
data. In ATASCII each character and graphics symbol , as well as
most of the control keys, has a number assigned to represent it.
The number is a one-byte code (decimal 0-255).
Backup DOS Disk: An exact copy of original master DOS
diskette . Always keep backups of your DOS master diskette and
of all important data diskettes.
BASIC: High-level programming language. Acronym for Begin-
ner's All-purpose Symbolic Instruction Code. BASIC is always
written using all capital letters. Developed by Mssrs. Kemeny
and Kurtz at Dartmouth College in 1963.
Baud Rate: Signalling speed or speed of information interchange in
bits per second.
BCD: Abbreviation for binary-coded decimal, a method of coding in
which each decimal digit is coded into a separate 4- bit word.
BCD is also known as the 8421 code due to the weight assigned to
each 4-bit word. The numbers used to count to ten are as follows:
DECIMAL
BINARY
1
1
BINARY
DECIMAL
10
2
11
3
100
4
101
5
110
6
111
7
1000
8
1001
9
1010
10
Binary: A number system using the base two. Thus the only
possible digits are and 1, which may be used in a computer to
represent true and false, on and off, etc.
Binary Arithmetic: Mathematical operations performed using
the binary digits of and 1.
Binary Load: Loading a binary machine-language object file into
the computer memory.
244
Binary Save— Bug
Binary Save: Saving a binary machine-language object file onto a
disk drive or program recorder.
Bit: Short for Binary Digit . A bit can be thought of as representing
or 1 , true or false , whether a circuit is on or off, or any other type
of two-possibility concept. A bit is the smallest unit of data with
which a computer can work. The word bit is a blend word formed
from "binary digit," a unit of information equal to one binary
decision. It can be a single character in a binary number, a single
pulse in a coded group of pulses , or a unit of information capacity .
When used as a unit of information capacity , the capacity in bits
is equal to the logarithm to the base two of the number of possible
states available. In a memory, for example, each element is
capable of representing a zero or a one at any instant, and the
total number of ones and zeros at any instant is the capacity of the
memory.
Boot: This is the initialization program that "sets up" the computer
when it is powered up. At conclusion of the boot (or after
"booting up"), the computer is capable of loading and executing
higher-level programs.
Branch: 1. ATARI BASIC executes a program in order of line
numbers. This execution sequence can be altered by the pro-
grammer, and the program can be told to skip over a certain
number of lines or return to a line earlier in the program. This
contrived change in execution sequence is called "branching" . 2.
The selection of one or more paths in the flow of data or signals
through a system or stage . Selection of a path is based upon some
criterion to allow a decision to be reached. The instructions used
to mechanize the selection are sometimes called branch instruc-
tions. Transfer of control and jump operations are also used in
this context. In a microprocessor program, branching is done on
the basis of computed results causing modification of the function
or program sequence. The usual modification can be classed as
(1) a change of the program direction, or (2) a departure from the
normal sequence.
Break: To interrupt execution of a program. Pressing the break
key causes a break in execution.
Buffer: A temporary storage area in RAM used to hold data for
further processing, input/output operations, etc.
Bug: A usually elusive error in a program, circuit, or machine.
245
Byte -Chip
Byte: Usually eight bits (enough to represent the decimal number
255 or 11111111 in binary notation) . A byte of data can be used to
represent an AT ASCII character or a number in the range of to
255. Byte is a generic term developed by IBM to indicate a
measureable number of consecutive binary digits which are usu-
ally operated upon as a unit. Bytes of eight bits representing
either one character or two numerals are most often encoun-
tered. Words in some systems are divided into high and low
bytes and the byte addresses are either odd or even numbers.
The high bytes are stored at the odd-numbered locations and the
low bytes at the even-numbered ones.
Cassette: A magnetic-tape housing that contains a tape of a specific
length. The cassette includes the supply reel, takeup reel, head
pressure pad, and a slot for the capstan drive.
Central Processing Unit (CPU): In microcomputers such as the
ATARI systems, these are also called microprocessors or MPU.
At one time, the CPU was that portion of any computer that
controlled the memory and peripherals . Now the CPU or MPU is
usually found on a single integrated circuit or "chip" (in ATARI'S
case a 6502 microprocessor chip) .
Character: A letter, numeral, or other symbol that is used to
express information. It is usually part of an ordered set and may
be graphic. Letters from English and other languages, any form
of numeral, all punctuation marks, and other formatting symbols
are all considered characters.
Character Code: An ordered pattern of bits that are assigned in a
particular system to represent characters . Baudot and ASCII are
character codes.
Chip: In its basic form, a chip is the integrated circuit inside an IC
housing. Those used in microcomputers typically utilize large-
scale integration techniques and up to 10,000 transistors have
been placed on chips of 6 mm square! The chips are usually
mounted in dual-inline packages which may have up to 40 pins for
mounting on circuit boards.
A microcomputer chip usually includes the arithmetic logic
unit (ALU) , general purpose register, and bus controls. The chip
of chips may also be combined with memory and input/output
chips to form a computer system that will fit on a single circuit
board.
246
CIO— Console
CIO: Central Input/Output Subsystem. The part of the operating
system that handles input/output.
CLOSE: To terminate access to a disk file. Before further access to
the file, it must be opened again. See Open.
Code: 1. (noun) Instructions written in a language understood by a
computer.
Code: 2. (verb) To write or form a routine in a computer program
using a system of rules and ordered characters which represent
symbols and characters from a different character set.
Coding: The process of converting program flowcharts into the
desired computer language.
Command: An instruction to the computer that is excuted im-
mediately. A good example is the BASIC command run. (See
Statement.)
Compiler: A coding or programming system that inputs source
language data and outputs a program either in assembly or
machine language. The compiler provides a language that re-
quires fewer statements for algorithm wiring and eliminates the
requirement for detailed coding to control loops, access data
structures, and write complex formulas and functions.
Computer: Any device that can receive and then follow instruc-
tions to manipulate information. Both the instructions and the
information may be varied from moment to moment. The dis-
tinction between a computer and a programmable calculator lies
in the computer's ability to manipulate text as well as numbers.
Most calculators can only handle numbers.
Computer Code: The machine language or code used with a
computer system.
Computer Program: The series of instructions and statements
prepared in order to solve a specific problem or achieve a certain
result.
Concatenation: The process of joining two or more strings to-
gether to form one longer string.
Console: The part of a computer system that is used for communi-
cation between the computer operator and the CPU. The com-
puter console may contain a start key , a stop key , a power control
switch, sense switches, and register lights. Other console func-
tions allow manual control, error correction, and status determi-
nation for counter and storage circuits. Some consoles allow the
programmer to debug the program by slowly stepping the
247
Console-CPU
machine through each instruction and observing the status indi-
cators; other consoles include a CRT terminal which may have
pictorial capabilities.
Constant: A fixed value or an item of data that does not vary.
Constants are those quantities or messages which are available
as data for the program and are not subject to change with time. A
constant can be one character or a group of characters which
represent a value and are used to identify , measure , or compare .
Control Characters: Characters produced by holding down the
key labeled CTRL while simultaneously pressing another key.
Control Console; A console that enables the operator to control
and monitor all processing functions from a central location. The
control console usually has a typewriter or other keyboard to
allow communication with the processor.
Controller: A unit which operates automatically to regulate the
performance of a controlled variable or system. Controllers use
the data from the input and the output of a device to obtain the
maximum and most efficient control of the device or process.
Controllers are also used in computer systems for generation of
signals to interface the CPU with memory and peripheral equip-
ment. A typical controller chip performs all the control functions
required for the flow of data at the interface.
Control Program: A sequence of instructions used to guide the
CPU through operations. A control program in a microprocessor
is usually stored in ROM where it can be accessed, but not
erased by the CPU.
Core Memory: A memory that uses toroids in matrix arrays for
storing binary digits. A core memory is a programmable
random-access memory that uses ferromagnetic storage
techniques.
Coupler: A device which transfers signals and has its input and
output isolated electrically. Also known as an isolator, a coupler
usually consists of a light-emitting diode (LED) and a light
sensor. The input signal activates the LED, which in turn forces
current through the output light sensor. When the two devices
are separated by an air gap rather than glass or plastic, the
coupler can be used to sense motion and encode cards, plates,
and slotted disks.
CPU: Abbreviation for central processing unit. A primary unit of
the computer system which controls the interpretation and
248
CPU-Decode
execution of instruction. A CPU may consist of registers, com-
putational circuits such as the arithmetic and logic unit, control
circuits, and input/output ports. The register may include ac-
cumulators, index registers, and perhaps stack registers. All
registers are treated as internal memory .
CRT: Abbreviation for "cathrode-ray tube" (the tube used in a TV
set). In practice, this is often used to describe the television
receiver used to display computer output. Also called a
"monitor". CRTs are used for both display and storage in com-
puter systems . As a display , the CRT can be operated in the point
mode to allow points to be established and displayed on the
screen. CRT storage uses the electron beam to sense the pres-
ence or absence of spots on the CRT screen.
Cursor: A square displayed on the TV monitor that shows where
the next typed character will be displayed. It is a manually
controllable pointer and can be employed to indicate a character
to be changed or corrected, or a position where data is to be
entered via the keyboard. The cursor may also take the form of an
underscore, an undertext caret, or an arrow.
Daisy Wheel: A plastic or metal print wheel on certain types of
impact printers, so called because of its symmetrical "petals."
Data: Information of any kind.
Debug: The process of locating and correcting mistakes and errors
in a program . Debugging involves the running and checking of
programs to detect any errors. One typical method of debugging
includes running a similar problem with a known answer through
the system checkout. Debugging aids are available to allow quick
development of microcomputer programs.
Decimal: A number base system using the digits through 9.
Decimal numbers are stored in binary-coded-decimal format in
the computer. See Bit, Hexadecimal, and Octal.
Decision: A determination of future action. A decision in computer
systems usually involves a comparison to determine the exis-
tence or nonexistence of a specific condition before taking a
specific succeeding action. The action may involve a conditional
jump or transfer of control. The comparison may take place
between words or numerical characters in registers or other
temporary storage.
Decode: The act of applying a set of data rules to restore a previous
representation, or to reverse a previous encoding operation.
249
Decoder— Disk file
Decoder: A device which determines the meaning of a set of data
and usually initiates some action based on the meaning. A de-
coder may be a matrix of switching elements used to select one
or more channels according to the combination of input signals.
Many decoder chips can be expanded so that each decoder drives
eight or more other decoders for large system applications.
Default: A mode or condition "assumed" by the computer until it is
told to do something else. For example, The ATARI will "de-
fault" to screen and keyboard unless told to use other I/O de-
vices. It will also default to GRAPHICS until another graphics
mode is entered.
Delimiter: A character that marks the start or finish of a data item
but is not part of the data. For example, the quotation marks (")
are used by most BASIC systems to delimit strings.
Destination: The device or address that receives data during an
exchange of information (and especially an I/O exchange) . See
Source.
Digital: Information that can be represented by a collection of bits.
Virtually all modern computers, especially microcomputers, use
the digital approach.
Digital-to-analog converter: A device for converting digital sig-
nals into continuous analog signals. Digital-to-analog converters
usually buffer the input so that the output remains the same until
the input changes. Units are available with up to 16 channels that
can operate at 10,000 samples per second with a 100-micro-
second conversion time.
Directory: A listing of the files contained on a diskette.
Discrete programming: A class of procedures used in operations
research for locating the maximum and minimum values of a
function. All variables must have integer values or similar con-
straints.
Diskette: A small disk. A record/playback medium like tape, but
made in the shape of a flat disk that is placed inside a stiff
envelope for protection. The advantage of the disk over cassette
or other tape for memory storage is that access to any part of the
disk is virtually immediate. The ATARI 800 Personal Computer
System can control up to 4 diskette drive peripherals simultane-
ously. In this book, disk and diskette are used interchangeably.
Disk file: An associated set of records of a similar format which can
be grounded by a common label and may be accessed as a unit.
250
Disk pack— Erase
Disk pack: Portable direct-address storage units which use
magnetic disks. Disk packs are mounted on disk storage drives
for read and write operations.
Disk storage: A memory system that stores data on magnetic
disks. The disks require a disk drive. Floppy disks, which are
used on the ATARI, are flexible and can store up to 300,000
words .
Display: A visual representation of data, which may take the form
of numerals , alphanumeric characters , or graphics . A display unit
can provide viewing access into the operation of the microcom-
puter system.
DOS: Abbreviation for "disk operating system". The software or
programs which facilitate use of a disk-drive system.
DOS. SYS: Filename reserved by Disk Operating System.
Drive Number: An integer from 1 to 4 that specifies the drive to be
used.
Drive Specification or Drivespec: Part of the filespec that tells
the computer which disk drive to access. If this is omitted the
computer will assume drive 1.
Edit: To make corrections or changes in a program or data.
Electronic digital computer: A machine which uses electronic
circuitry to perform arithmetic and logic operations by means of
an internally or externally stored program of machine instruc-
tions.
Electronic pen: A stylus that is used with a CRT display for input
to the system computer. Also called a light pen, the stylus
signals the computer with electronic pulses which the computer
interprets.
Encoder: Any device or circuit that provides an enabling code to
permit an otherwise unusable system or device to be used in an
environment where the code is required. In a selective calling
communications system, an encoder may be a simple tone oscil-
lator of a specific frequency.
End of File: A marker that tells the computer that the end of a
certain file on disk has been reached.
Entry Point: The address where execution of a machine-language
program or routine is to begin . Also called the transfer address .
Erase: To clear or obliterate information in a storage medium.
Erasing results in the replacement of all digits with zeros in
251
Erase —Flowchart
magnetic storage. Erasing in some EPROMs is done with a
specified level of ultraviolet light.
Execute: To do what a command or program specifies. To run a
program or portion thereof.
Expression: A combination of variables, numbers, and operators
(+, -, etc.) that can be evaluated to a single quantity. The
quantity may be a string (sexp) or a number (aexp) .
Fetch: 1. To locate and load a program from storage, as in bringing
a program phase into main storage for execution from the mem-
ory library. 2. That portion of a computer cycle from which the
location of the next instruction is obtained. A fetch can also be
used to retrieve phases of a program and load them into main
storage, or transfer control to a system loader.
File: An organized collection of related data. A file is the largest
grouping of information that can be addressed with a single name .
For example , a BASIC program is stored on diskette as a par-
ticular file, and may be addressed by the statements save or load
(among others).
Filename: The alphanumeric characters used to identify a file. A
total of 8 numbers and/or letters may be used. The first of these
must be a letter.
Filename Extender or Extension: From 1 to 3 additional
characters used following a period (required if the extender is
used) after the filename. For example, in the filename PHON-
LIST.BAS. the letters "BAS" comprise the extender.
Filespec: Abbreviation for file specification. A sequence of
characters which specifies a particular device and filename. Do
not create two files with exactly the same filespec. If you do, and
they are both stored on the same diskette, you will not be able to
access the second file, and the DOS functions of delete file,
rename file, and copy file will act on both files.
Flip-flop: A circuit that is capable of assuming either one of two
stable states; a bistable multivibrator. It will assume a given
state depending upon the previous history of the inputs.
Floppy Disks: A magnetic storage medium that uses flexible disks
that resemble phonograph records . Each one can provide random
access storage for as much as 163,000 or more bytes, (double
density) and are used to replace cassettes in many applications .
Flowchart: A graphical representation of the definition or solution
252
Flowchart— Graphic display
of a problem, in which symbols are used to represent functions,
operations, and flow. It can contain all of the logical steps in a
routine or program in order to allow the designer to concep-
tualize and visualize each step . It defines the major phases of the
processing, as well as the path to problem solution.
Format: 1. (noun) A predetermined arrangement of data, words,
letters, characters, files, etc. 2. (verb) To specify the form in
which something is to appear. 3. To organize a new or magnet-
ically (bulk) erased diskette into tracks and sectors. When for-
matted , each diskette contains 40 circular tracks , with 18 sectors
per track. Each sector can store up to 128 bytes of data (single
density), or 256 bytes of data (double density).
Gap: A space or interval which appears between items of data. A
magnetic gap refers to the air space in the magnetic circuit. A
head gap refers to the separation between the pole pieces of a
magnetic recording head. A data gap may appear as an interval of
space or time to indicate the end of a word , record , or file on tape ,
or it may be the complete absence of information for a length of
time or space on the recording medium.
Gate: A circuit or device having one output and one or more inputs
with the output state completely determined by the previous and
present states of the inputs. A gate can also be a trigger used to
allow the passage of other signals through a circuit. Logical gates
can take many forms.
Get: To locate, fetch, and transfer an item from storage, (the
activity required to develop or make a record from an input file
available) , or to obtain or extract a coded value from a field . The
get command might be used to obtain a numerical value from a
series of decimal digits.
Goto: A multilanguage statement that directs the computer to leave
the current sequence of instructions and begin operating at
another point in the program. A typical BASIC goto instruction
might be:
goto 5; (the next statement to be executed is number 5)
Graphic: 1. Any assembly of symbols or characters that is used to
denote any concept, configuration, or idea non-textually. 2. Any
symbol produced by printing, drawing, handwriting, etc.
Graphic display: A nontextual display which reproduces data on a
video screen, panel, or page.
253
Halt— Information bits
Halt: A condition occurring after the sequence of operations in a
program stops. A halt may be due to a halt (stop) instruction, an
unexpected halt, or an interrupt. The program would normally
continue after the halt unless a "drop-dead" halt occurs. In this
case there is no recovery . The drop-dead halt may be a part of the
program designed to shut down the system , or it may be due to an
error in programming such as division by zero, or transfer to a
nonexistent instruction.
Hard Copy: Printed output as opposed to temporary TV monitor
display.
Hardware: The physical components of a computer system, in-
cluding all electronic and electromechanical devices and connec-
tions .
Hardware assembler: An assembler that usually consists of
PROMs which are mounted on simulation boards. A hardware
assembler allows the prototype unit to assemble its own pro-
grams.
Hexadecimal or Hex: Number base system using 16 alpha-
numeric characters: 0, 1,2,3,4, 5, 6, 7,8,9, A, B, C,D,E,and
F.
Hold: A condition which suspends operation of a system or circuit
for a specified time.
Hold instruction: An instruction which causes data called from
storage to be retained after it is called out.
Imprinter: A device for marking characters onto a form . Imprint-
ers include typewriters, printers, presses, pressure plates, and
stamping machines.
Increment: Increase in value (usually) by adding one. Used a lot
for counting (as in counting the number of repetitions through a
loop) .
Index: 1. A symbol or number used to identify a specific quantity in
an array of similar items. 2. An ordered reference list of the
contents of a file with keys for identification of the contents and
the action required in preparing such a list. 3. In numerical
control, movement of a machine part to a predetermined loca-
tion.
Information bits: Any bits that are generated by the data source
and not used for error control . Information theory provides that
all information can be represented by some collection of bits,
254
Information bits— Instruction
regardless of the complexity of the information.
Initialize: To set to an initial or starting value; to do the prelimi-
nary steps that are not to be repeated, such as setting counters
and addresses to zero. In ATARI BASIC, all nonarray variables
are initialized to zero when the command run is given. Array and
string elements are not initialized.
Input: 1. (noun) Information transferred to the computer. Output is
information transferred away from the computer. In this manual,
input and output are always in relation to the computer. 2. (verb)
To transfer data from outside the computer (say, from a diskette
file) into RAM. Output is the opposite, and the two words are
often used together to describe data transfer operations: Input/
Output or just "I/O". Note that the reference point is always the
computer.
Input device: A device or set of devices used to bring data into
another device. An input may be a channel for impressing or
inserting a state or condition on another device, or a device or
process involved in an input operation.
Input/output: Pertaining to either input or output or both. It is
abbreviated I/O.
Input/output channel: A circuit path which allows independent
communication between the processor and external devices.
Input/output channels may transfer data between memory and
external interfaces in blocks of any size without disturbing
working registers in the processor. Multiple channels are al-
lowed to operate concurrently with hardware priority control of
each channel . Transfers are in full words , with automatic packing
and unpacking allowed in some systems.
Instruction: A statement containing information which can be
coded and used as a unit in a digital computer to command it to
perform one or more operations . An instruction usually contains
one or more addresses and may specify arithmetic operations
such as addition or multiplication, or control operations for data
manipulation. Instructions can be grouped as:
1. Data transfers between registers and memory.
2. Branching operations .
3. Input/output control.
4. Loading and storing accumulators.
5. Restoring registers and accumulators.
6. Jumps and stack-pointer operations.
255
Instruction— Keyboard
7. Binary and decimal arithmetic.
8. Set and reset interrupts.
9. Increment and decrement registers and memory.
Instruction code: All of the symbols and definitions used to
systematize the instructions for a given computer or executive
routine .
Integrated circuit: An interconnected array of components,
which is fabricated from a single crystal of semiconductor mate-
rial by etching, doping, and diffusion, and which is capable of
performing at least one and sometimes many complete circuit
functions.
Interactive: A system that responds quickly to the user, usually
within a second or two. All personal computer systems are
interactive .
Interface: The electronics used to allow two devices to communi-
cate. An interface enables devices to exchange information and
implies a connection to complete the interchange.
Interpreter: An executive routine which translates a stored pro-
gram written in a high-level language into machine code and
performs the indicated operations using subroutines as they are
translated.
I/O: Short for input/output, I/O devices include the keyboard, TV
monitor, program recorder, printer, and disk drives.
IOCB: Input/ Output Control Block. A block of data in RAM that
tells the operating system the information it needs to know for an
I/O operation. It is written as an arithmetic expression equal to a
number between 1 and 7.
I/O test program: Refers to a special PROM containing a program
which plugs into the checks input/output circuit boards.
Item size: The magnitude of an item expressed in words, charac-
ters, or blocks.
K: Stands for "kilo" meaning "times 1000". Thus 1 Kbyte is (ap-
proximately) 1000 bytes. (Actually 1024 bytes.) Also, the device
type code for the keyboard.
Keyboard: A unit containing keys for entering data or information
into a system . Keyboards may be alphanumeric (as used for word
processing, text processing, and data processing) or numeric as
used for Touch-Tone telephones, accounting machines, and cal-
culators .
256
Keyword— List
Keyword: A word that has meaning as an instruction or command
in a computer language, and thus must not be used as a variable
name or at the beginning of a variable name.
Kilobyte or K: 1024 bytes of memory. Thus a 16K RAM capacity
actually gives us 16*1024 or 16,384 bytes.
Language: A set of conventions specifying how to tell a computer
what to do. A language consists of a carefully defined set of
characters and rules for combining the characters into larger
units such as words or expressions . There are also rules for word
arrangement and usage to achieve specific meanings . Most com-
puter languages have the following features:
1 . Data objects or structures with descriptions that correspond
to nouns and adjectives in natural languages.
2 . Operations and commands which act upon the data objects ,
corresponding to verbs and adverbs in a natural language.
3. Control structures to specify the sequence of operations
which correspond to phrasing and forming paragraphs in natural
languages .
Language interpreter: A processor, assembler, or other routine
that accepts statements in one language and produces equivalent
statements in another language.
Language translator: A program or routine that converts state-
ments in one language to equivalent statements in another lan-
guage. The languages may be computer or machine languages, or
natural languages such as English.
Least significant byte: The byte in the rightmost position in a
number or a word.
Light pen: A photosensitive device that can cause the computer to
change or modify the display on a CRT screen or can be used to
enter input into a program. As the display information is selected
by the operator, the light pen signals the computer using a pulse.
The computer can then instruct other points or lines to be plotted
on the screen following the pen movements, or can utilize the
input in the program.
List: An ordered set of items. A pushdown list is a set of items in
which the last item entered is the first item in the list, and the
position of the other items is pushed back by one. A pushup list
has items entered at the end of the list, and the other items
maintain the same relative position in the list.
257
Load— Matrix printer
Load: The process of filling a storage unit in a computer. Loading
includes the reading of the beginning of a program into storage
and the modifications necessary to the program for the transfer of
control for execution. Loading also includes the transfer of stor-
age between memory units . A typical load operation transfers
the contents of a memory byte and stores it in the accumulator.
The memory is read bit by bit, and as each bit is read, the next
sequential accumulator bit will be set or reset to reproduce the
status of the memory bit just read.
Logic gates: A circuit or single component capable of performing a
logic operation. A gate may have several inputs but only one
output.
Loop: A self-contained series of instructions in which the final
instruction can modify itself, causing the process to be repeated
until a terminal condition is reached. Productive instructions in
the loop are used to manipulate operands while housekeeping or
bookkeeping instructions modify the productive instructions and
keep track of the number of operations and repetitions. A loop
may be terminated under any number of conditions.
Machine: A general term for a device such as a microprocessor
or microcomputer that can store and process numeric and al-
phabetic information. Machine is used to refer to both analog and
digital computers along with related data processing equipment.
Machine-code: An operation code that a machine is designed to
recognize directly and without translation.
Machine language: A language that can be used directly by a
microprocessor; a binary language. All other languages must be
translated or compiled into binary code before entering the
processor. Users generally write the program in coded instruc-
tions that are more meaningful to them. Then assembly pro-
grams are used to translate the symbolic instructions into binary
machine code.
Magnetic core storage: A storage system that uses a core of
magnetic material coupled by wires or other conductors. The
cores are magnetized to represent binary ones or zeros.
Matrix printer: A device that uses an array of dots to form
characters. Dot-matrix character formation is also used in some
display devices. Sometimes called dot matrix printer.
258
Memory— Microprocessor
Memory: The part of a computer (usually RAM or ROM) that
stores data or information.
Memory bus: The circuit path for communication between the
CPU and memory. A memory bus may actually consist of three
buses which are time-shared over a single bus:
1. Memory address bus.
2. Memory-to-CPU data bus.
3. CPU-to-memory data bus.
Memory scan: An option which provides a rapid search of any part
of memory for any word. With a memory-scan option, any block
of locations may be searched using a single instruction.
Menu: A list of options from which the user may choose.
Microcomputer: A computer based on a microprocessor chip; in
ATARI'S case, the 6502. A microcomputer is a complete small
computing system consisting of hardware and software. The
hardware includes the microprocessing unit, memory, auxiliary
circuits, power supply, and control panel. The main processing
blocks are typically fabricated with large-scale integration circuit
packages.
A typical microcomputer has the CPU on a single chip or circuit
board; the system also contains ROM storage for programs and
data along with clock circuits, input and output units, selector
registers, and control circuits. The console control panel typi-
cally has a typewriter- type keyboard. The keyboard is an input
port. Standard software often includes an assembler, loader,
source editor, and debugging and diagnostic routines.
Microprocessor: The large-scale integration equivalent of a com-
puter's central processing unit , designed to work as a sequential
computational or control unit by executing a defined set of in-
structions contained in memory . In a microcomputer with a fixed
instruction set, the microprocessor may consist of an arith-
metic-logic unit and a control-logic unit. In a microcomputer with
a microprogrammed logic set, it may contain an additional
control-memory unit . The microprocessor determines what de-
vices should have access to data and makes these decisions based
upon timing requirements. It also correlates the activities of the
memory and input/output units.
All microprocessors use large-scale integrated circuit tech-
nology; some feature a single-chip construction while others use
259
Microprocessor— Monitor system
several chips. The division or partitioning of functions is based
on considerations of word length, flexibility, and performance.
Microprogramming: The techniques of modifying an instruction
set by building higher-level instructions from basic elemental
operations. The higher-level instructions can then be directly
programmed. If a machine has basic instructions for addition,
subtraction, and multiplication, an instruction for division could
be defined by microprogramming. Microprogramming adds
flexibility to the microcomputer. Compared to conventional
programming, the distinctive feature is the storage associated
with the control unit. In microprogramming, a user instruction
determines an address in control memory which provides the
starting point for executing the microprogrammed steps .
Microprogramming enhances flexibility by allowing the
machine to optimize its control memory for specific applications.
This ability to adjust can greatly simplify programming. It is
generally slow, since each user instruction requires that a se-
quence of programmed steps be executed. Control storage ROM
must be fast enough to allow the use of a separate clock that is
five to ten times faster than that used for main memory .
Mnemonic: 1 . A word-like symbol used in assembly languages to
cause a computer to execute an instruction whose description
resembles the word symbol. The term MOV A, B is a mnemonic
for "move the contents of register B into arithmetic register A."
Modem: An electronic device that performs the modulation and
demodulation functions required for communications. A modem
(formed from a blending of modulator and demodulator) can be
used to connect computers and terminals over telephone cir-
cuits. On the transmission end, the modulator converts the
signals to the correct codes for transmission over the communi-
cations line. At the receiving end, the demodulator reconverts
the signals for communication to the computer using the com-
puter interface unit.
Monitor: The television receiver used to display computer output.
Monitor system: The hardware and software used to control
computer system functions. The monitor system can simulate
the processor, maintain continuity between jobs, observe and
report on the status of input/output devices, and provide au-
tomatic accounting of jobs.
260
Most Significant Byte— Numerical control
Most Significant Byte: The byte in the leftmost position in a
number or a word .
Multiplier: A device that generates a product from two numbers. A
digital multiplier generates the product from two digital numbers
by additions of the multiplicand in accordance with the value of
the digits in the multiplier. It then shifts the multiplicand and
adds it to the product if the multiplier digit is a one, or shifts
without adding if the digit is a zero. This is done for each
successive digit of the multiplier.
NOR: A logical operation that has a true output only if all inpu s are
zero (false). The negative-OR operation.
NOT: A logic operator having the property : if P is a statement , then
the NOT of P is true if P is false; and it is false if P is true. The
NOT operator is represented by an overline.
NOT AND: The NAND operation.
NOT AND gate: An AND gating circuit combined with an inverter;
a NAND gate.
Notation: The act, process, or method used to represent technical
facts or quantities. In computer practice, the term typically
describes the number radix, as follows:
NOTATION RADIX
BINARY 2
TERNARY 3
QUATERNARY 4
QUINARY 5
DECIMAL 10
DUODECIMAL 12
HEXADECIMAL 16
DUOTRICENARY 32
BIQUINARY 2,5
NOT if-then gate: A gate that performs the A AND NOT B and B
AND NOT A operations.
Null String: A string consisting of no character whatever. For
example, A$="" stores the null string as A$.
Numerical control: The automatic control of a machine or process
using numerical data that is introduced using punched tapes or
other input methods. Most numerical-control devices have lim-
ited logical capability, and they rely on the input medium for
261
Numerical control— Operator console
detailed guidance. A computer is generally used to prepare the
control media.
Object code: Machine language derived from "source code," typi-
cally from Assembly Language.
Octal: The octal numbering system uses the digits through 7.
Address and byte values are sometimes given in octal form.
One-address: A system of instructions such that each complete
instruction explicitly describes one operation and one storage
location.
Open: To prepare a file for access by specifying whether an input or
output operation will be conducted, and specifying the filespec.
Operand: 1 . The fundamental quantity on which a mathematical
operation is performed. A statement usually consists of an
operator and an operand; in an add instruction, the operator will
indicate "add," and the operand will indicate what is to be added.
2. A result, parameter, or the address portion of an instruction.
Operating console: A unit which contains all controls and indi-
cators necessary for the operation of the processor. A typical
microcomputer operating console may include the following
functions:
1 . Run indicator and switch
2. Halt indicator and switch
3. Reset switch
4. Link indicator
5. Interrupt indicator
6. Accumulator program counter, and memory display
Operation code: A code that represents specific actions. Also
called instruction code.
Operation decoder: A device that selects one or more channels of
operation according to the operator part of the machine instruc-
tion.
Operator: 1. The mathematical symbol which represents the pro-
cess to be performed on an associated operand. 2. The portion of
an instruction which indicates the action to be performed on the
operands.
Operator console: A hardware unit which allows the operator to
communicate with the computer. The operator console is used to
enter data or information, to request and display stored data, and
to actuate the various command routines.
262
OR— Precedence
OR: A logic operator having the following property for logical
quantities P and Q:
p
Q
PORQ
1
1
1
1
1
1
1
The OR operator is represented in electrical terminology by a
"plus" symbol.
OR ELSE: A logical operator which states that if P and Q are
statements , then P OR ELSE Q is either true or false . Also called
EITHER/OR.
OS: Abbreviation for operating system. This is actually a collection
of programs to aid the user in controlling the computer.
Output: The produced signals used to drive peripheral terminals.
See I/O.
Paging: The procedure used to locate and transmit pages between
main storage and auxiliary storage, or to exchange them with
pages of the same program or other programs. Paging can be
used to assist in the allocation of a limited amount of main storage
among several concurrent programs.
Parallel: Two or more things happening simultaneously. A parallel
interface, for example, controls a number of distinct electrical
signals at the same time. Opposite of serial.
Pen light: A pen-like device with light and a photosensor on one
end for communicating with a computer through a CRT device.
Peripheral: An I/O device. See I/O.
Permutation: Any one of the total number of changes in position or
form that are possible in a group.
Pilot system: A collection of file records and data obtained from a
business over a period of time and used for simulation purposes.
Pip: A spot of light on a CRT screen for display pointing, calibra-
tion.
Pixel: Picture Element. One point on the screen display. Size
depends on graphics mode being used.
Precedence: Rules that determine the priority in which operations
are conducted, especially with regard to the arithmet-
ical/logical operators.
263
Problem language— Programming
Problem language: The language used by a programmer in stat-
ing the definition of a problem.
Processor: A hardware data processor or a program that performs
the functions of compiling, assembling, and translating for a
specific language. Processor operations can involve registers,
accumulators, program counters and stacks, and input/output
and internal instruction control .
Processor module: The circuit card that contains the micro-
processor along with the logic and control circuitry necessary to
operate as a processing unit. The processor support circuits
consist of clock circuits, multiplexer, bus control, input/output
control, and interrupt logic.
Program: 1. A set of instructions arranged in the proper se-
quence for directing the computer in performing a desired oper-
ation, such as the solution of a mathematical problem or the
sorting of data. 2. To prepare a set of ordered instructions for
automatic computer operation.
A program includes plans for the transcription of data, coding
for the computer, and plans for the absorption of results into the
system.
Program counter: A counter which contains the address of the
next instruction to be fetched from memory. The address is
automatically incremented after an instruction fetch except when
modified by branch instructions. During interrupts, the program
counter saves the address of the instruction.
Program error: A mistake made in the program code by the
programmer, keypuncher, compiler, or assembler.
Program library: A collection of available computer programs and
routines. A typical microcomputer library might include a text
editor, loader, assembler, RAM test program, decimal addition,
PROM programmer, A/D conversion, logic subroutines, and
BCD-to-binary conversion.
Programmable logic: Devices and systems which provide logic
functions that can be changed by the user. Programmable logic
devices include FPLAs, PLAs, ROMs, EAROMs, RAMs,
CAMs, and microprocessors. Programmable logic systems in-
clude microcomputers, programmable calculators, minicomput-
ers, and large-scale computers.
Programming: The design, writing, and testing of programs.
Programming may consist of:
264
Programming— Random number generator
1. Definition of problem.
2. Preparation of flowchart.
3. Listing of computer instructions .
4. Selecting circuit patterns or control modes.
Programming flowchart: A flowchart used to represent the
sequence of operations in a program.
Prompt: A symbol that appears on the monitor screen that indi-
cates the computer is ready to accept keyboard input. In ATARI
BASIC, this takes the form of the word "READY". A "?" is also
used to prompt a user to enter (input) information or take other
appropriate action.
Pseudo code: A code that requires translation prior to execution.
Pseudo codes are often used to link a subroutine into the main
routine, and they usually express programs in terms of source
language by referring to locations and operations using symbolic
names and addresses.
Pseudo instruction: A group of characters having the same gen-
eral form as an instruction, but never executed as an actual
instruction. Pseudo instructions are used as symbolic represen-
tations in compilers, interpreters, and assemblers to designate
groups of instructions for performing a particular task.
RAM: Abbreviation for random-access memory. The main memory
in most computers. RAM is used to store both programs and
data. It is a mass store that provides fast access to any storage
location point. A RAM system can be divided into three main
sections:
1. Address buffers, read- write logic, and chip-select logic.
2. Data bus buffers and memory array.
3. Refresh and control logic.
During a cycle, a 1 on a write input/output line will be inter-
preted by the RAM as a write enable command, and data on the
bus will be written in. Available RAMS have access times from 2
nanoseconds to 3 seconds and range in size from 4 to 4096 bits
per chip.
Random number generator: May be hardware (as is ATARI's) or
a program that provides a number whose value is difficult to
predict. Used primarily for decision-making in game programs,
etc.
265
Record— Selector
Record: A block of data.
Reserved word: See Keyword.
Reset: To return a device such as a register to zero or to an initial
or selected condition.
Restore: To return an index, address, word, or character to its
initial state, sometimes by periodic recharge or regeneration.
ROM: Abbreviation for read-only memory. In this type of solid-
state electronic memory, information is stored by the manufac-
turer and it cannot be changed by the user. Programs such as the
BASIC interpreter and other cartridges used with the ATARI
systems use ROM.
Routine: An ordered set of instructions used to direct the com-
puter to perform one or more specific tasks or operations. A
closed routine is one that is not entered as a block of instructions
within the main routine, but entered by a linkage from the main
routine. A routine may be considered as a subdivision of a
program with two or more instructions that are functionally
related.
Run: The execution of a program on or of several routines linked
together so that they form an operating unit. Usually during a
run, manual operations are minimal; a typical run may involve
loading, reading, processing, and writing.
Save: To copy a program or data into some location other than RAM
(for example, diskette or tape).
Screen: The TV screen, In ATARI BASIC, a particular I/O device
codes "S:"
Sector: The smallest block of data that can be written to a disk file
or read from one. Sectors can store up to 128 bytes (single
density) or 256 bytes (double density).
Segment: 1. To divide a routine into parts with each one capable of
being completely stored in internal storage and containing the
necessary instructions to jump to other segments . 2 . A part of a
routine short enough to be sorted entirely in the internal storage
of a computer, yet containing the coding necessary to call in and
jump to other segments. A segment can be placed anywhere in
memory and addressed relative to a common origin.
Selector: 1. A switching operation based on previous processing
which allows a logical choice to be made in the program or
system. 2. A mechanical multiposition switch. 3. Cursor.
266
Separator— Storage
Separator: A specific character used to mark the logical boundary
between items that can be considered as separate and distinct
units.
Serial: The opposite of parallel. Things happening only one at a
time in sequence. Example: A serial interface.
Shift instruction: A computer instruction which causes the con-
tents of an accumulator register to shift to the right or left. A
right shift instruction is equivalent to dividing by two; a left shift
instruction is equivalent to multiplying by two, or adding the
contents of the register to itself.
Signal: The intelligence , message , or effect to be conveyed over a
transferal system; it may be electrical , visual , or audible . It is the
event or phenomenon for conveying the data from one point to
another.
Software: As opposed to Hardware. Refers to programs and data.
Software package: The programs or sets of programs used in a
particular application or function. Many software packages in-
clude diagnostic programs for verifying processor and memory
operation along with cross-assemblers.
Software system: The entire set of programs and software de-
velopment aids used in a microcomputer system.
Source: The device or address that contains the data to be sent to a
destination.
Source code: A series of instructions, written in language other
than machine language, which requires translation in order to be
executed.
Special character: A character that can be displayed by a com-
puter but is neither a letter nor a numeral. The ATARI graphics
symbols are special characters. So are punctuation marks, etc.
Specific routine: A routine used to solve a particular arithmetic,
logic, or data-handling problem in which each address refers to
explicitly stated registers and locations.
Statement: An instruction to the computer. See also Command.
While all commands may be considered statements, all state-
ments are certainly not commands. A statement contains a line
number (deferred mode) , a keyword, the value to be operated on,
and the RETURN command.
Storage: A device or medium on or into which data can be entered,
held, and retrieved later; a memory. Storage may use electro-
267
Storage— Track
static, magnetic, acoustic, optical, electronic, or mechanical
methods.
String: (1) A sequence of letters , numerals and characters which
may be stored in a string variable. The string variable's name
must end with a $. (2) Any linear sequence of items which are
grouped in a series according to certain rules . A string may be a
set of records grouped in ascending or descending sequence
according to a key contained in the records.
Subroutine: A part of a program that can be executed by a special
statement (gosub) in BASIC . A subroutine can be a portion of
another routine which allows the computer to carry out a defined
mathematical or logical operation. This effectively gives a single
statement the power of a whole program. The subroutine is a
very powerful construct.
System data bus: A bus designed for communications between all
external units and the CPU. A typical bus transfers information
between any two devices connected to the bus by granting access
through a priority network for bus control .
System handbook: A document that provides a concise reference
of all the major characteristics of the microcomputer system.
The system handbook will contain operation codes, addressing
modes, service status details, interfaces, timing diagrams, and
data flow.
Termination: The end of a program or program run.
Text editing: An editing facility designed into a text-editing pro-
gram to allow the keyboard entry of text or copy without regard
to the final format. After the copy has been placed in storage, it
can be edited and justified by specifying the desired format.
Tokenizing: The process of interpreting textual BASIC source
code and converting it to the internal format used by the BASIC
interpreter.
Trace routine: A routine used to provide a time history of machine
registers and controls during the execution of the object routine .
A complete tracing routine can provide the status of all registers
and locations affected by each instruction each time the instruc-
tion is executed.
Track: A circle on a diskette used for magnetic storage of data.
Each track has 18 sectors, each with 128 byte storage capability
(single density) . There are a total of 40 tracks on each diskette .
268
Variable— Zone Bit
Variable: A variable may be thought of as a box in which a value
may be stored. Such values are typically numbers and strings.
Visual display terminal: This is a device that permits inputs to a
computer system through a keyboard or other manual terminal or
input device such as a light pen, and whose primary output is
visual through a CRT unit or other type of display. The terminals
allow keyboarding, verification, editing, correction, and refor-
matting of material.
Window: A portion of the TV display devoted to a specific purpose
such as for graphics or text.
Word processing: The preparation of printed material using au-
tomatic data processing equipment.
Write-Protect: A method of preventing the disk drive from writing
on a diskette . ATARI diskettes are write-protected by covering a
notch on the diskette cover with a small sticker.
Zone Bit: A bit in a group of positions used to indicate a specific
class of items or, in some cases, a bit used as a key to a code.
269
Index
Access time, 28
Addition, binary, 31-35
Addresses, 81
Algebra, Boolean, 44-79
Analog computers, 12
AND (Boolean operation), 50, 51
AND (Boolean term), 46, 47
Arithmetic, computer, 17, 31-43
Arithmetic functions, 14, 15, 143, 144
Arithmetic-logic unit, 16
Assembly language programming,
199, 200
ATASCII character set, 229
B
BASIC, 81,82, 107
BASIC commands, 127-131
BASIC language cartridge, 107
BASIC programming statements,
87-96
BASIC reserved words, directory,
220-225
BCD code, 1 1
Binary arithmetic, 31-43
Binary coded decimal, 10
Binary codes, 10
Binary digit, 4
Binary number codes, 198
Binary numbers, 1
Binary number system, 3, 4
Bits, 3
Boolean algebra applications to
switching circuits, 49-58
Boolean algebra laws, 56-59
Boolean classes, 46, 47
Boolean element, 46, 47
Boolean equation mechanization
59-79
Boolean equation simplification, 59-79
Boolean expressions, relational, 44,
45
Boolean operations, 44-79
Boolean symbols, 47-49
Bus, address, 27
Bus, computer, 26, 27
Bus, control, 27
Bus, data, 27, 28
Bus systems, 26, 27
Cassette recorder, loading programs
from the, 118
Cassette recorder, saving programs
on the, 116-118
Cathode ray tube, 17
Celsius-Fahrenheit temperature con-
version, 83-88
Central processing unit, 16
Checkbook balancer program, 161-
164
Chip, 25, 26
Chips, 12
Clock, master, 28, 29
Codes, 1
Commands, graphic, 174-192
Commands, input /output, 138-142
Commands, sound, 192, 193
Complements, Boolean, 53
Computer blues program, 195
Computer components, 97-106
Computer elements, basic, 15-17
Computers, analog, 12
Computers, digital, 12, 15
Computer structure, 15-17
Continuing education, 205-219
Control, 16, 17, 19, 20
Control characters, printed versions,
238
Controllers, 121, 122
Conversions between number sys-
tems, BCD to decimal, 1 1
Conversions between number sys-
tems, binary to decimal, 7
Conversions between number sys-
tems, binary to hexadecimal, 9,
10
Conversions between number sys-
tems, binary to octal, 7
Conversions between number sys-
tems, decimal to binary, 4-7
Conversions between number sys-
tems, decimal to binary deci-
mals, 40-43
Conversions between number sys-
tems, decimal to octal, 8
Conversions between number sys-
tems, octal to decimal, 8
CPU, 25
Currency exchange program, 1 49-1 51
Cartridges, program, 98, 99
Cassette input /output, 140, 141
Cassette recorder, 105, 106, 137
Data manipulation, 19-23
Data storage, 20, 21
Decimal number system, 1-3
270
DeMorgan's Theorem, 76, 79
Derived functions, 237
Digital computers, 12, 15
Direct memory access, 26
Disk drives, 122-134, 137, 138
Diskettes, 123
Disk operating system (DOS), 124-
127
Disk operations, 127-134
Disk operations, BASIC commands
used with, 127-131
Disk utility package (DUP), 124, 125
Division, binary, 39, 40
E
Edit features, 102-105
Education, computer, 205-219
Elements, interconnection, 18
Error messages, BASIC, 131-134
Exclusive OR, 56
F
File management subsystem (FMS),
126, 127
File names, 126
Flowcharts, 84-86, 165-173
Fractions, binary, 40-43
Functions, arithmetic, 143, 144
Functions, computer, 12, 13
Functions, derived, 237
Functions, secretarial, 13
Functions, special purpose, 145, 146
Functions, trigonometric, 144
G
Glossary, 242
Graphics, 174-192
Graphics commands, 174-186
Graphics modes, 174-177
Graphics modes, color, 176, 177
Graphics window, 177
Greatest common divisor program,
157-159
Gun collector program, 159-161
H
Hardware, 15
Hexadecimal numbers, 1
Hexadecimal number system, 8-10
Hexcode loader program, 200
High-level language, 81
I
IC, 25, 26
ICs, dedicated, 26
Input, 16
Input/output commands, 138-142
Input /output devices, 137, 138
Inputs, computer, 15, 16
Instructions, arithmetic-logic, 18
Instructions, control, 18
Instructions, data movement, 18
Instructions, input/output, 18
Integer, 2
Instruction set, 18
Integrated circuits, 25, 26
Interconnection of computer ele-
ments, 18
Interface, RS-232, 138
IOCB (input /output control block),
137
I /O operations, 135-142
J
Joystick, 122
Keyboard, 99-105, 137
Keyboard input/output, 141
Keys, special, 99-105
Large-scale computers, 23, 24
Laws of Boolean algebra, 56-59
Learning to program, 108-116
Lessons, correspondence, 208-219
Light show program, 188
Line numbers, 88, 89
M
Machine language, 198-204
Margins, 175
Master bus control, 27
Master element, 27
Mathematics, binary, 31-43
Maxterms, Boolean, 47
McGraw-Hill Continuing Education
Center, 205
Medium-scale computers, 24
Memory, computer, 14, 16
Memory locations, 239
Memory map, 234-236
Memory modules, 97, 120
Memory saving techniques, 147, 148
Metric conversion program, 151-156
Microcomputer basics, 12
Microcomputers, 24, 25
Microcomputers, one chip, 26
Microcomputer terms, 242
Microprocessors, 23, 25, 26
Minicomputers, 24
Minterms, Boolean, 47
Multiplication, binary, 37-39
Multiply instruction, 18
271
NAND (Boolean operation), 55
National Technical Schools, 205, 207
NOR (Boolean operation), 53-55
NRI (correspondence school), 205
Number systems, 1
Number systems, binary, 3, 4
Number systems, decimal, 1-3
Number systems, hexadecimal, 8-10
Number systems, octal, 7, 8
Number systems and codes, 1
Octal numbers, 1
Octal number system, 7, 8
OR (Boolean operation), 52
OR (Boolean term), 47
Output devices, 15
Outputs, computer, 17
P
Paddle, 121, 122
Pathways, bidirectional, 19
Pathways, data, 19, 23, 26, 27
Peripherals, 97, 106, 119-134
Printer, 137
Printer input /output, 141, 142
Printers, 119, 120
Program, checkbook balancer, 161-
164
Program, computer blues, 195
Program, currency exchange, 149-
151
Program, greatest common divisor,
157-159
Program, gun collector, 159-161
Program, hexcode loader, 200
Program, light show, 188
Program, metric conversion, 151-156
Program, text modes character print,
186
Program, type a tune, 193
Program, United States flag, 189
Program, video graffiti, 190
Programming, 80-96
Programming, purposes for, 106
Programming, simple steps in, 108-
116
Programming in machine-language,
198-204
Programming objectives, 82
Programming statements, BASIC, 87,
90,96
Programming steps, 82-88
Program recorder, 105, 106, 137
Programs, computer, 13, 15
Programs, sample, 149-156
Pseudocode, 173
Radix, 1
RAM, 30, 107
Random-access memory, 30
Read command, 20, 21
Read-only memory, 30
Register, 20
Registers, storage, 28
ROM, 30, 98, 107
RS-232 interface, 138
Saving programs on tape, 116-118
Schools, correspondence, 205-208
Screen editor, 138
Screen output, 142
Size, computer, 23-26
Slave element, 27
Software, 15, 17, 18
Sound, 192-197
Sound commands, 192, 193
Special purpose functions, 145, 146
Storage, computer, 17
Storage types, kinds of, 30
Subtraction, binary, 36, 37
Symbology, Boolean, 47-49
Techniques, flowcharting, 165-173
Temperature conversion program,
83-88
Text modes character print program,
186
Text window, 177
Transistors, 12
Trigonometric functions, 144
TV monitor, 138
Type a tune program, 193
U
United States flag program, 189
USR function, 198
Veitch diagrams, 61-76
Venn diagrams, 47, 49-56
Video graffiti program, 190
W
Write command, 20, 21
Writing to storage, 27, 28
XOR (Boolean operation), 56
272
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